The Tongue

The dorsal surface of the tongue is divided by the sulcus terminalis into an oral part, the anterior two-thirds, and a pharyngeal part, the posterior one-third. The dorsal surface of the oral part has a characteristic appearance due to the presence of a large number of small projections, the lingual papillae. The epithelium of the pharyngeal part forms a somewhat irregular surface which covers the lingual tonsils.

The lingual papillae consist of a connective tissue core covered with a stratified squamous epithelium. On the basis of their appearance four types of papillae can be distinguished - filiform, fungiform, circumvallate and foliate papillae.

The muscles of the tongue (skeletal muscle) are organized into strands oriented more or less perpendicular to each other. Their actions provide the tongue with the necessary motility to participate in the formation of speech and to aid in the initial processing of foods.

Filiform papillae

Fungiform papillaeFungiform papillae

Circumvallate papillaeCircumvallate papillae

Foliate papillaFoliate papilla • are not well developed in humans and are not well developed in humans and

may be absent in aged individualsmay be absent in aged individuals. .

Taste BudsTaste Buds Taste buds are most numerous in the fungiform, Taste buds are most numerous in the fungiform,

circumvallate and foliate papillaecircumvallate and foliate papillae. . In addition, taste buds In addition, taste buds are found in the palate, palatoglossal and are found in the palate, palatoglossal and palatopharyngeal arches and in the pharynx and larynxpalatopharyngeal arches and in the pharynx and larynx..

In histological sections they appear as ovoid lightly stained In histological sections they appear as ovoid lightly stained bodies, which extend perpendicular from the basement bodies, which extend perpendicular from the basement membrane to a little opening formed in the epithelium, the membrane to a little opening formed in the epithelium, the taste poretaste pore. . The elongated cells that form the taste bud can The elongated cells that form the taste bud can functionally be divided into three groupsfunctionally be divided into three groups: : sensory cells, sensory cells, supporting supporting ((or sustentacularor sustentacular) ) cells, and basal cellscells, and basal cells. . Sensory Sensory cells extend microvilli into the taste porecells extend microvilli into the taste pore. . These microvilli These microvilli contain the receptors for the different basic taste contain the receptors for the different basic taste modalities modalities ((sweet, salty, bitter and acidsweet, salty, bitter and acid). ). Basal cells Basal cells regenerate the two other cell typesregenerate the two other cell types

Salivary Glands

Saliva is a mixed secretion, which is derived from numerous large and small salivary glands that all open into the oral cavity. Small salivary glands are situated in the connective tissue beneath the epithelia lining the oral cavity, and, in the case of the tongue, they may also be found between the muscular tissue. Depending on the localisation they are grouped into lingual, labial, buccal, molar and palatine glands.

The large salivary glands form three paired groups:

1.the sublingual glands, which are positioned beneath the tongue and embedded deeply in the connective tissue of the oral cavity,

2.the submandibular glands and

3.the parotid glands, which lie outside the oral cavity.

All of these glands are tubuloacinar glands, i.e. they have secretory acini but the first part of the duct system originating from the acini also participates in the secretory process. The salivary glands are divided by connective tissue septa into lobes, which are further subdivided into lobules.

Functionally the secretory acini can be divided into two groups: those that secrete a rather liquid product - serous acini, and those that secrete a very viscous product - mucous acini. This functional differentiation is reflected in the appearance of these acini in histological sections.

Occasionally, and In particular in glands located relatively close to the oral cavity, serous cells and mucous cells may form compound or mixed acini. The serous cells form in these cases small half-moon or crescent-shaped structures, which attach to mucus producing acini and empty their secretory product into interstices between the mucus-producing cell. Following their appearance they are called serous demilunes.

Ducts of the Salivary Glands

The ducts of the salivary glands can, according to their position in relation to the lobes and lobules of the glands, be divided into two parts. Interlobular and interlobar ducts are embedded in the connective tissue surrounding the lobes and lobules of the glands. Interlobar and interlobular ducts function mainly in the conduit of the saliva and are formed by a stratified cuboidal or stratified columnar epithelium. The epithelium is replaced by the stratified squamous epithelium as they approach the opening into the oral cavity.

The product of serous glands is extensively modified by the initial part of the duct system. Intralobular ducts can on the basis of their function be divided into intercalated ducts and striated ducts. The secretory acini empty into intercalated ducts which merge into the striated ducts.

Esophagus

In the oesophagus the mucosa is formed by a stratified squamous epithelium (non-keratinised) .

Oesophageal glands are located in the submucosa. These submucosal glands produce a mucous secretion, which lubricates the epithelium and aids the passage of food. The mucous glands in the part of the oesophagus closest to the stomach protect the oesophageal mucosa from acidic reflux from the stomach. Mucous glands in the adjacent mucosa of the stomach are called cardiac glands, and this name is also used for submucosal mucosal glands in the the part of the oesophagus closest to the stomach.

The Stomach

The stomach functions both as a reservoir and as a digestive organ. It empties its contents in small portions (suitable for continued digestion) into the small intestine.

Anatomically, the stomach is divided into :

1- a cardiac part,

2- fundus,

3- body or corpus, and

4- a pyloric part (pyloric antrum and pyloric canal)

Histologically, most of the layers of the wall of the stomach appear similar in its different parts. Regional differences are mainly restricted to the appearance of the gastric mucosa.

Types of stomach cells Types of stomach cells ((4 types4 types)) 1 - Chief cells (or zymogenic cells)

are the most numerous of the four types. They occur primarily in the body of the glands. They produce pepsinogen, which is a precursor of the proteolytic enzyme pepsin.The pH optimum of of pepsin is about 2. This enzyme is able to break down collagen.

2- Parietal cells (or oxyntic cells) occur most frequently in the neck of the glands, where they reach the lumen of the gland. They are situated deeper, between and below chief cells, in lower parts of the gland. Parietal cells secrete the hydrochloric acid of the gastric juice. Aside from activating the pepsinogen the hydrochloric acid also effectively sterilizes the contents of the stomach.

Parietal cell also secrete intrinsic factor, which is necessary for the resorption of vitamin B12

Note that so far only one type of bacteria has found which can live happily in the stomach - Helicobacter pylori. Unfortunately these bacteria are involved in the pathogenesis of gastritis and gastric ulcers.

3- Mucous neck cells

are found between the parietal cells in the neck of the gland.

They are difficult to distinguish from chief cells in plain H&E stained section

4- Endocrine cells

are scattered, usually solitary, throughout the epithelium of the gastrointestinal tract. They are part of the gastro-entero-pancreatic (GEP) endocrine system.

Small Intestine

The small intestine is divided into duodenum (25-30 cm), jejunum(2.5 m) and ileum(3.5m ). The three segments merge imperceptibly and have the same basic histological organization.

Between the intestinal villi we see the openings of simple tubular glands, the crypts or glands of Lieberkühn. They extend through the lamina propria down to the muscularis mucosae.

Paneth cells are located at the bottom of the crypts. They release a number of antibacterial substances, among them lysozyme, and are thought to be involved in the control of infections.

One function of the crypts of Lieberkühn is the secretion of "intestinal juice" (about 2 liter/day).

Large Intestine

The large intestine constitutes the terminal part of the digestive system. It is divided into three main sections: 1- cecum including the appendix

2- colon,

3- rectum with the anal canal. The primary function of the large intestine is the reabsorption of water and inorganic salts. The only secretion of any importance is mucus, which acts as a lubricant during the transport of the intestinal contents.

The crypts are long ,straght , and contain large numbers of goblet cells , thry lack paneth cells .

The vermiform appendix

is a small blind-ending diverticulum from the cecum. The most important features of the appendix is the thickening of its wall, which is mainly due to large accumulations of lymphoid tissue in the lamina propria and submucosa. Intestinal villi are usually absent, and crypts do not occur as frequently as in the colon. There is often fatty tissue in the submucosa. The muscularis externa is thinner than in the remainder of the large intestine and, the outer, longitudinal smooth muscle layer of the muscularis externa does not aggregate into taenia coli.

The Pancreas

is positioned retroperitoneally on the posterior wall of the abdominal cavity at the level of the second and third lumbar vertebrae.

has no distinct capsule, but is covered by a thin layer of loose connective tissue.

is both an exocrine and endocrine gland. The exocrine part produces about 1.5 l of pancreatic juice every day. The endocrine part, which accounts for ~1% of the pancreas, consists of the cells of the islands of Langerhans. These cells produce insulin, glucagon and a number of other hormones.

Pancreatic juice is a clear alkaline fluid which contains the precursors of enzymes of all classes necessary to break down the main components of the diet as trypsin and chymotrypsin .

Components of the exocrine Components of the exocrine pancreas pancreas

The exocrine pancreas consists of The exocrine pancreas consists of tubuloacinar glandstubuloacinar glands. . A single layer of pyramidal shaped cells forms the A single layer of pyramidal shaped cells forms the secretory acinisecretory acini. . The apical cytoplasm The apical cytoplasm ((towards the towards the lumen of the acinilumen of the acini) ) is filled with secretory vesicles is filled with secretory vesicles containing the precursors of digestive enzymescontaining the precursors of digestive enzymes. . The The first portion of the duct system extends into the centre first portion of the duct system extends into the centre of the acini, which is lined by of the acini, which is lined by small small centroacinar centroacinar cellscells. . These cells form the first part of These cells form the first part of intercalated ductsintercalated ducts. . Intercalated ducts are lined Intercalated ducts are lined by low columnar or cuboidal epitheliumby low columnar or cuboidal epithelium. . They They empty into interlobular ducts, which are lined empty into interlobular ducts, which are lined by a columnar epitheliumby a columnar epithelium. . Interlobular ducts in Interlobular ducts in turn empty into the turn empty into the main pancreatic ductmain pancreatic duct ( (of of WirsungWirsung)), which is lined by a tall columnar , which is lined by a tall columnar epitheliumepithelium..

Components of the Endocrine Components of the Endocrine Pancreas Pancreas

Islands of Langerhans, usually containing Islands of Langerhans, usually containing several hundred endocrine cells, are several hundred endocrine cells, are scattered throughout the exocrine tissue scattered throughout the exocrine tissue of the pancreasof the pancreas. . The vascularization, The vascularization, composed of many fenestrated composed of many fenestrated capillaries, is more extensive than that of capillaries, is more extensive than that of the exocrine tissuethe exocrine tissue..

Although the quantitative cellular Although the quantitative cellular composition of the islands is quite composition of the islands is quite variable, we find typicallyvariable, we find typically::

75% beta75% beta--cells which secrete cells which secrete insulininsulin.. 20% alpha20% alpha--cells which secrete cells which secrete glucagonglucagon 5% delta5% delta--cells which secrete somatostatin cells which secrete somatostatin

The Liver

is the largest gland of the body (about 2% of the body weight in an adult).

receives both venous blood, through the portal vein (~75% of the blood supply), and arterial blood, through the hepatic artery (~25% of the blood supply).

is surrounded by a well defined but thin capsule of connective tissue.

functions as an exocrine gland because it secretes bile.

An idealized representation of the "classical" liver lobule is a six-sided

-Anatomy of the liver (short note )

-Vessels of the liver

-Function of the liver ( Metabolic and storage functions)

Bilary systemBilary system Terminal bile ducts are lined by a cuboidal epitheliumTerminal bile ducts are lined by a cuboidal epithelium. . All other parts All other parts

of the bilary system are lined by a tall columnar epitheliumof the bilary system are lined by a tall columnar epithelium. . In the In the gall bladder the epithelium is often folded and gall bladder the epithelium is often folded and ""cavedcaved". ". The gall The gall bladder functions in the storage and concentration of bilebladder functions in the storage and concentration of bile. . Microvilli Microvilli on the apical surface of the epithelial cells facilitate the resorption of on the apical surface of the epithelial cells facilitate the resorption of water from the bilewater from the bile..

The epithelium lining the biliary system does not contain mucusThe epithelium lining the biliary system does not contain mucus--producing cells and a muscularis mucosae is absentproducing cells and a muscularis mucosae is absent. . These features These features allow you to distinguish the gall bladder from other parts of the allow you to distinguish the gall bladder from other parts of the gastrointestinal tractgastrointestinal tract..

Many of the components of bile are not secretory products of the Many of the components of bile are not secretory products of the hepatocytes in a strict sensehepatocytes in a strict sense. . They are reabsorbed in the gut and return They are reabsorbed in the gut and return to the liver through the portal veinto the liver through the portal vein. . Here they are taken up by the Here they are taken up by the hepatocytes and excreted again hepatocytes and excreted again - - a phenomenon called enterohepatic a phenomenon called enterohepatic circulationcirculation..

TracheaThe trachea is a fairly short tube (10-12 cm) with a diameter of ~2 cm.Epithelium, Mucosa and Submucosa

The trachea is stabilized by 16-20 C-shaped or horseshoe- shaped cartilages (hyaline cartilage). The trachea is lined by respiratory epithelium. The number of goblet cells is variable and depends on physical or chemical irritation of the epithelium which increase goblet cell number. In addition to the staple of basal cells, ciliated cells and goblet cells , the respiratory epithelium also contains brush cells, endocrine cells (or small granule cells, function not clear), surfactant-producing cells (or Clara cells), and serous cells.Epithelium and underlying lamina propria are called the mucosa. The lamina propria consists of loose connective tissue with many elastic fibres, which condense at the deep border of the lamina propria to form an elastic membrane. This elastic membrane forms the border between the mucosa and the connective tissue below it, which is called the submucosa. Muco-serous glands in the submucosa (submucosal glands) supplement the secretions of cells in the epithelium.. Tracheal cartilages The free dorsal ends of the cartilages are connected by bands of smooth muscle (trachealis muscle) and connective tissue fibres.

Conductive Structures in the Lung

BronchiIn the lungs we find the last segments of the conductive portion of the respiratory system. The histological structure of the epithelium and the underlying connective tissue of the bronchi corresponds largely to that of the trachea and the main bronchi. In addition, bronchi are surrounded by a layer of smooth muscle, which is located between the cartilage and epithelium.

BronchiolesBronchioles are the terminal segments of

the conductive portion. At the transition from bronchi to bronchioles the epithelium changes to a ciliated columnar epithelium, but most of the cell types found in the epithelium of other parts of the conductive portion are still present. Glands and cartilage are absent. The layer of smooth muscle is relatively thicker than in the bronchi.

Respiratory Structures in the LungRespiratory Structures in the Lung Bronchioles divide into Bronchioles divide into respiratory bronchiolesrespiratory bronchioles, which are the first structures that , which are the first structures that

belong to the respiratory portion of the respiratory systembelong to the respiratory portion of the respiratory system. . Small outpouchings of Small outpouchings of the walls of the respiratory bronchioles form the walls of the respiratory bronchioles form alveolialveoli, the site of gas exchange, the site of gas exchange. . The The number of alveoli increases as the respiratory bronchioles continue to dividenumber of alveoli increases as the respiratory bronchioles continue to divide. . They They terminate interminate in alveolar ductsalveolar ducts. . The The ""wallswalls" " of alveolar ducts consists of entirely of of alveolar ducts consists of entirely of alveolialveoli..

Histological Structure of AlveoliHistological Structure of Alveoli The wall of the alveoli is formed by a thin sheet The wall of the alveoli is formed by a thin sheet ((~2µm~2µm) ) of tissue separating two of tissue separating two

neighbouring alveolineighbouring alveoli. . This sheet is formed by epithelial cells and intervening This sheet is formed by epithelial cells and intervening connective tissueconnective tissue. . Collagenous Collagenous ((few and finefew and fine)), reticular and elastic fibres are , reticular and elastic fibres are presentpresent. . Between the connective tissue fibres we find a Between the connective tissue fibres we find a dense, anastomosing dense, anastomosing network of pulmonary capillariesnetwork of pulmonary capillaries. . The wall of the capillaries are in direct contact The wall of the capillaries are in direct contact with the epithelial lining of the alveoliwith the epithelial lining of the alveoli. .

The epithelium of the alveoli is formed by two cell typesThe epithelium of the alveoli is formed by two cell types:: Alveolar type I cellsAlveolar type I cells ( (small alveolar cells or type I pneumocytessmall alveolar cells or type I pneumocytes) ) are extremely are extremely

flattened flattened ((the cell may be as thin as 0.05 µmthe cell may be as thin as 0.05 µm) ) and form the bulk and form the bulk ((9595%) %) of the of the surface of the alveolar wallssurface of the alveolar walls. . The shape of the cells is very complex, and they may The shape of the cells is very complex, and they may actually form part of the epithelium on both faces of the alveolar wallactually form part of the epithelium on both faces of the alveolar wall..Alveolar type II cellsAlveolar type II cells ( (large alveolar cells or type II pneumocyteslarge alveolar cells or type II pneumocytes) ) are irregularly are irregularly ((sometimes cuboidalsometimes cuboidal) ) shapedshaped. . They form small bulges on the alveolar wallsThey form small bulges on the alveolar walls. . Type II Type II alveolar cells contain are large number of granules called alveolar cells contain are large number of granules called cytosomescytosomes ( (or or multilamellar bodiesmultilamellar bodies)), which consist of precursors to pulmonary surfactant , which consist of precursors to pulmonary surfactant ((the the mixture of phospholipids which keep surface tension in the alveoli lowmixture of phospholipids which keep surface tension in the alveoli low) . ) . There are There are just about as many type II cells as type I cellsjust about as many type II cells as type I cells. . Their small contribution to alveolar Their small contribution to alveolar area is explained by their shapearea is explained by their shape. .

Cilia are absent from the alveolar epithelium and cannot help to remove particulate Cilia are absent from the alveolar epithelium and cannot help to remove particulate matter which continuously enters the alveoli with the inspired airmatter which continuously enters the alveoli with the inspired air. . Alveolar Alveolar macrophagesmacrophages take care of this job take care of this job. . They migrate freely over the alveolar epithelium They migrate freely over the alveolar epithelium and ingest particulate matterand ingest particulate matter. . Towards the end of their life span, they migrate Towards the end of their life span, they migrate either towards the bronchioles, where they enter the mucus lining the epithelium to either towards the bronchioles, where they enter the mucus lining the epithelium to be finally discharged into the pharynx, or they enter the connective tissue septa of be finally discharged into the pharynx, or they enter the connective tissue septa of the lungthe lung..

Reticular and elastic fibres form the bulk of the connective tissue present in the walls of the alveoli

URINARY SYSTEMURINARY SYSTEM The kidneys, ureters, urinary bladder and urethra The kidneys, ureters, urinary bladder and urethra

are the main components of the urinary systemare the main components of the urinary system excretion of waste products from the bodyexcretion of waste products from the body. . This is This is

only one of many functions of the systemonly one of many functions of the system. . Others Others are :are :

elimination of foreign substances elimination of foreign substances regulation of the amount of water in the body regulation of the amount of water in the body control of the concentration of most compounds control of the concentration of most compounds

in the extracellular fluid in the extracellular fluid

Functionally the processes can be divided into Functionally the processes can be divided into two steps :two steps :

filtration filtration - - glomeruli of the kidney glomeruli of the kidney selective resorption and excretion - tubular selective resorption and excretion - tubular

system of the kidney system of the kidney In addition, the kidney also functions as an In addition, the kidney also functions as an

endocrine organendocrine organ. . Fibrocytes Fibrocytes in the cortex in the cortex release the hormone release the hormone erythropoietinerythropoietin, which , which stimulates the formation of red blood cellsstimulates the formation of red blood cells. . Modified fibrocytesModified fibrocytes of the medulla secrete of the medulla secrete prostaglandins prostaglandins which are able to decrease which are able to decrease blood pressureblood pressure..

Glomeruli and the tubular system are both part of the Glomeruli and the tubular system are both part of the basic functional unit of the kidney, basic functional unit of the kidney, the the nephronnephron..

The Glomerulus (Bowman’s)or renal corpuscle)The Glomerulus (Bowman’s)or renal corpuscle)

The glomerulus is the round (~0.2 mm in diameterThe glomerulus is the round (~0.2 mm in diameter glomerulus is enclosed by two layers of epithelium, glomerulus is enclosed by two layers of epithelium, Bowman's Bowman's

capsulecapsule. Cells of the outer or . Cells of the outer or parietal layerparietal layer of Bowman's capsule of Bowman's capsule form a simple squamous epithelium. Cells of the inner layer, form a simple squamous epithelium. Cells of the inner layer, podocytespodocytes in the in the deep layerdeep layer, are extremely complex in shape. , are extremely complex in shape.

Small foot-like processesSmall foot-like processes

Tubules of the NephronTubules of the Nephron The tubular system can be divided into The tubular system can be divided into

proximal and distal tubulesproximal and distal tubules, which in turn , which in turn have have convoluted and straight portionsconvoluted and straight portions. . Intermediate tubulesIntermediate tubules connect the proximal connect the proximal and distal tubules. Running from the and distal tubules. Running from the cortex of the kidney towards the medulla cortex of the kidney towards the medulla (descending), then turning and running (descending), then turning and running back towards the cortex (ascending), back towards the cortex (ascending), the the tubules form the tubules form the loop of Henleloop of Henle

UretUretersers the paired ureters carry urine from the renal pelvis of the paired ureters carry urine from the renal pelvis of

the kidney to the urinary bladder , The basic structure the kidney to the urinary bladder , The basic structure of all these components is the same. The mucosa is of all these components is the same. The mucosa is lined with a lined with a transitional epitheliumtransitional epithelium The mucosa is lined The mucosa is lined with a transitional epitheliumwith a transitional epithelium , which occurs exclusively , which occurs exclusively in the urinary system their tissue layers are :The in the urinary system their tissue layers are :The lamina propria consists mainly of dense connective lamina propria consists mainly of dense connective tissue, with many bundles of coarse collagenous fibres. tissue, with many bundles of coarse collagenous fibres. The muscularis usually consists of an inner longitudinal The muscularis usually consists of an inner longitudinal and outer circular layer of smooth muscle cells . In and outer circular layer of smooth muscle cells . In lower parts of the ureter and the bladder an additional lower parts of the ureter and the bladder an additional outer longitudinal layer of muscles is added to the first outer longitudinal layer of muscles is added to the first

two.two.

The bladder is finally emptied The bladder is finally emptied through the urethrathrough the urethra. . Initially, the Initially, the urethra is lined by a transitional urethra is lined by a transitional epithelium in males and females epithelium in males and females

THE INTEGUMENTARY SYSTEMTHE INTEGUMENTARY SYSTEM The skin or covers the entire outer surface of the body. Structurally, The skin or covers the entire outer surface of the body. Structurally,

the skin consists of two layers which differ in function, histological the skin consists of two layers which differ in function, histological appearance and their embryological origin. The outer layer or appearance and their embryological origin. The outer layer or epidermisepidermis is formed by an epithelium and is of ectodermal origin. is formed by an epithelium and is of ectodermal origin. The underlying thicker layer, the The underlying thicker layer, the dermisdermis, consists of connective , consists of connective tissue and develops from the mesoderm. Beneath the two layers we tissue and develops from the mesoderm. Beneath the two layers we find a subcutaneous layer of loose connective tissue or find a subcutaneous layer of loose connective tissue or hypodermishypodermis, , which binds the skin to underlying structures. Hair, nails and sweat which binds the skin to underlying structures. Hair, nails and sweat and sebaceous glands are of epithelial origin and collectively called and sebaceous glands are of epithelial origin and collectively called the the appendages of the skinappendages of the skin..

The skin and its appendages together are called the The skin and its appendages together are called the integumentary integumentary

systemsystem..

The EpidermisThe Epidermis The epidermis is a The epidermis is a keratinised stratified squamous epitheliumkeratinised stratified squamous epithelium. The main function of . The main function of

the epidermis is to protect the body from harmful influences from the environment the epidermis is to protect the body from harmful influences from the environment and against fluid loss. Five structurally different layers can be identified:and against fluid loss. Five structurally different layers can be identified:

1-The stratum basale1-The stratum basaleis the deepest layer of the epidermis (closest to the dermis). It is the deepest layer of the epidermis (closest to the dermis). It consists of a single layer of columnar or cuboidal cellsconsists of a single layer of columnar or cuboidal cells 2-2- the the stratum spinosumstratum spinosum,,the cells become irregularly polygonal the cells become irregularly polygonal

3-The stratum granulosum3-The stratum granulosum consists, in thick skin, of a few layers of flattened cellsconsists, in thick skin, of a few layers of flattened cells 4--4--The The stratum lucidumstratum lucidum

consists of several layers of flattened dead cells. (The stratum consists of several layers of flattened dead cells. (The stratum lucidum can usually not be identified in thin skin.)lucidum can usually not be identified in thin skin.)   

5-5-the the stratum corneumstratum corneum,,cells are completely filled with keratin filaments (horny cells) which cells are completely filled with keratin filaments (horny cells) which are embedded in a dense matrix of proteins are embedded in a dense matrix of proteins

Other Cells of the Epidermis : Melanocytes The brown colour component is due to melanin, which

is produced in the skin itself in cells called melanocytes These cells are located in the epidermis and send fine processes between the other cells. In the melanocytes, the melanin is located in membrane-bound organelles called melanosomes.

Langerhans Cells are another cell type found within the epidermis. They are

important in immune reactions of the epidermis T-lymphocytes are, like Langerhans cells, a group of

cells functioning in the immune system.

The DermisThe Dermis The dermis is the thick layer of The dermis is the thick layer of

connective tissue to which the epidermis connective tissue to which the epidermis is attached. is attached.

The dermis may be divided into two The dermis may be divided into two sublayers :sublayers :

1-The 1-The papillary layerpapillary layer consists of loose, consists of loose, comparatively cell-rich connective tissue, comparatively cell-rich connective tissue, which fills the hollows which fills the hollows

2-The 2-The reticular layerreticular layer appears denser and appears denser and contains fewer cells contains fewer cells

Sweat GlandsSweat Glands Two types of sweat glands are present in humans. They are distinguished by their secretory

mechanism into merocrine (~eccrine) sweat glands and apocrine sweat glands. In addition, they differ in their detailed histological appearance and in the composition of the sweat they secrete.

Merocrine sweat glands are the only glands of the skin with a clearly defined biological function. They are of critical importance for the regulation of body temperature. The skin contains ~3,000,000 sweat gland which are found all over the body

Sweat glands are simple tubular glands. The secretory tubulus and the initial part of the excretory duct are coiled into a roughly spherical ball at the border between the dermis and hypodermis.

The secretory epithelium is cuboidal or low columnar. A layer of myoepithelial cells is found between the secretory cells of the epithelium and the

basement membrane. The excretory duct has a stratified cuboidal epithelium (two layers of cells). The excretory ducts of merocrine sweat glands empty directly onto the surface of the skin. Apocrine sweat glands occur in, for example, the axilla. They are stimulated by sexual

hormones and are not fully developed or functional before puberty. Apocrine sweat is a milky, proteinaceous and odourless secretion. The odour is a result of bacterial decomposition and is, at least in mammals other than humans, of importance for sexual attraction.

The histological structure of apocrine sweat glands is similar to that of merocrine sweat glands, but the lumen of the secretory tubulus is much larger and the secretory epithelium consists of only one major cell type, which looks cuboidal or low columnar. Apocrine sweat glands as such are also much larger than merocrine sweat glands.

The excretory duct of apocrine sweat glands does not open directly onto the surface of the skin. Instead, the excretory duct empties the sweat into the upper part of the hair follicle. Apocrine sweat glands are therefore part of the pilosebaceous unit.

ENDOCRINE GLANDSENDOCRINE GLANDS Endocrine (or internally secreting) glands Endocrine (or internally secreting) glands

are also named ductless glands, since are also named ductless glands, since they lack excretory ducts. Instead, the they lack excretory ducts. Instead, the secretory cells release their products, secretory cells release their products, hormoneshormones, into the extracellular space, into the extracellular space

The major endocrine glands are :The major endocrine glands are : The pituitary glandThe pituitary gland The thyroid glandThe thyroid gland The parathyroid gland The parathyroid gland The adrenal glandsThe adrenal glands The pancreasThe pancreas

Pituitary GlandPituitary Gland

The pituitary gland (or hypophysis) is The pituitary gland (or hypophysis) is attached to the inferior surface of the attached to the inferior surface of the brainbrain

the pituitary gland can be divided into: the pituitary gland can be divided into: Neurohypophysis, and adenohypophysis Neurohypophysis, and adenohypophysis adenohypophysis can be divided into a adenohypophysis can be divided into a pars intermedia and a pars distalis.pars intermedia and a pars distalis.

Cells and secretary products of the hypophysisCells and secretary products of the hypophysis::

AdenohypophysisAdenohypophysis

The pars distalis of the adenohypophysis accounts for about 75% of the hypophyseal The pars distalis of the adenohypophysis accounts for about 75% of the hypophyseal tissue tissue

glandular cells are subdivided into : glandular cells are subdivided into : chromophobe cells chromophobe cells acidophil cellsacidophil cells basophil (chromophil) cellsbasophil (chromophil) cells

Chromophobe cellsChromophobe cells

Chromophobe cells are unstained or weakly stained cells. Most chromophobe cells can be assigned to the different classes of chromophils if EM and immunocytochemistry are used

Acidophil cells (or acidophils)Acidophil cells (or acidophils)

Acidophils are rounded cells and typically smaller than basophil cells.Acidophils are rounded cells and typically smaller than basophil cells.

Acidophils account for roughly 65% of the cells in the adenohypophysisAcidophils account for roughly 65% of the cells in the adenohypophysis

-The most frequent subtype of acidophils are the somatotrophs -The most frequent subtype of acidophils are the somatotrophs

-Somatotrophs produce growth hormone (GH or somatotropin).-Somatotrophs produce growth hormone (GH or somatotropin).

Basophil cells (or basophils)Basophil cells (or basophils)

Based on their hormone products basophils are divided into three subtypesBased on their hormone products basophils are divided into three subtypes

1-Thyrotrophs produce thyroid stimulating hormone (TSH or thyrotropin). 1-Thyrotrophs produce thyroid stimulating hormone (TSH or thyrotropin).

2-Gonadotrophs produce follicle stimulating hormone (FSH)2-Gonadotrophs produce follicle stimulating hormone (FSH) and luteinizing hormone (LH) and luteinizing hormone (LH)

3-Corticotrophs 3-Corticotrophs ((or adrenocorticolipotrophsor adrenocorticolipotrophs) ) secrete adrenocorticotropic hormone secrete adrenocorticotropic hormone ((ACTH ) ACTH )

THYROID GLANDTHYROID GLAND

The thyroid gland is situated on the lateral sides of the The thyroid gland is situated on the lateral sides of the lower part of the larynx and upper part of the trachea. The lower part of the larynx and upper part of the trachea. The size is quite variable but typically ranges around 20g size is quite variable but typically ranges around 20g (slightly larger in females than in males).(slightly larger in females than in males).

The thyroid gland consists almost entirely of rounded cysts, The thyroid gland consists almost entirely of rounded cysts, follicles.follicles.

It consists of a simple cuboidal epithelium which surrounds It consists of a simple cuboidal epithelium which surrounds a lumen filled with a viscous substance, colloida lumen filled with a viscous substance, colloid

The colloid is the secretory product of the follicular cell .The colloid is the secretory product of the follicular cell . The size of the follicles is variable ranging from about 50 The size of the follicles is variable ranging from about 50

µm to about 1 mm.µm to about 1 mm.

Hormones of the thyroid glandHormones of the thyroid gland The main secretory products of the The main secretory products of the

thyroid gland are thyroxine and thyroid gland are thyroxine and triiodothyronine triiodothyronine

PARATHYROID GLANDSPARATHYROID GLANDS

The parathyroid glands are four small oval bodies located at The parathyroid glands are four small oval bodies located at the posterior surface of the thyroid gland the posterior surface of the thyroid gland

-These glands are small (average total weight is about 130 mg.-These glands are small (average total weight is about 130 mg. Capillaries are abundantCapillaries are abundant. A considerable number of fat cells . A considerable number of fat cells

infiltrate the gland (beginning around puberty) and may infiltrate the gland (beginning around puberty) and may account for about half the weight of the parathyroid glands account for about half the weight of the parathyroid glands in adults.in adults.

Two cell types can be distinguished in the parathyroid glands:Two cell types can be distinguished in the parathyroid glands:

1-Chief cells1-Chief cells are the most numerous type. They are rather small, a round, are the most numerous type. They are rather small, a round, light and centrally placed nucleus and a very weakly acidophilic light and centrally placed nucleus and a very weakly acidophilic cytoplasm. They synthesise parathyroid hormone (PTH )cytoplasm. They synthesise parathyroid hormone (PTH )

2-Oxyphilic cells2-Oxyphilic cells are less frequent (entirely lacking in small children; are less frequent (entirely lacking in small children; occurring first in children six to seven years old and afterwards occurring first in children six to seven years old and afterwards increasing in number with age .increasing in number with age .

ADRENAL GLANDSADRENAL GLANDS

The adrenal glands consist of an outer cortex (the main part of The adrenal glands consist of an outer cortex (the main part of the adrenal glands) and an inner medulla (which accounts the adrenal glands) and an inner medulla (which accounts for about 10% of the adrenal glands). The gland is for about 10% of the adrenal glands). The gland is surrounded by a thick connective tissue capsule. Cortex and surrounded by a thick connective tissue capsule. Cortex and medulla are two distinct endocrine organs .medulla are two distinct endocrine organs .

CortexCortex The cortex is divided into three concentric zones which, from the The cortex is divided into three concentric zones which, from the

surface inwards, are termed the zona glomerulosa (accounting for surface inwards, are termed the zona glomerulosa (accounting for about 15% of the cortical thickness), the zona fasciculata (about 75%) about 15% of the cortical thickness), the zona fasciculata (about 75%) and the zona reticularis (about 10%). and the zona reticularis (about 10%).

Cells of the zona glomerulosa are organised into small rounded Cells of the zona glomerulosa are organised into small rounded groups or curved columns. Cells are smaller than in the two other groups or curved columns. Cells are smaller than in the two other zones, their nuclei are dark and round, and the cytoplasm is light zones, their nuclei are dark and round, and the cytoplasm is light basophilic.basophilic.

The zona fasciculata consists of radially arranged cell cords located The zona fasciculata consists of radially arranged cell cords located centrally. The cytoplasm is also light and often has a characteristic centrally. The cytoplasm is also light and often has a characteristic foamy or spongy appearance they are for this reason also called foamy or spongy appearance they are for this reason also called spongiocytes. spongiocytes.

Anastomosing cell chords separated by sinusoid spaces form the zona Anastomosing cell chords separated by sinusoid spaces form the zona reticularis. Cells are typically smaller than in the zona fasciculata. reticularis. Cells are typically smaller than in the zona fasciculata. Their cytoplasm is eosinophilic and less spongy than that of other Their cytoplasm is eosinophilic and less spongy than that of other cells in the cortex.cells in the cortex.

Hormones produced in the cortex are Hormones produced in the cortex are all steroids: aldosterone, cortisolall steroids: aldosterone, cortisol

MALE REPRODUCTIVE SYSTEMMALE REPRODUCTIVE SYSTEM

The internal male genitalia consist of :The internal male genitalia consist of :

-The testes -The testes

-The vas deferens -The vas deferens

-The seminal vesicles -The seminal vesicles

-The prostrate-The prostrate

TestesTestes

The testes have, like the ovaries, two The testes have, like the ovaries, two functions: they functions: they produce the male produce the male gametes or spermatozoa, and they gametes or spermatozoa, and they produce male sexual hormone, produce male sexual hormone, testosteronetestosterone, which stimulates the , which stimulates the accessory male sexual organs and accessory male sexual organs and causes the development of the causes the development of the masculine extragenital sex masculine extragenital sex characteristics.characteristics.

The testes have, like the ovaries, two functions: The testes have, like the ovaries, two functions: they produce the male gametes or they produce the male gametes or spermatozoa, and they produce male sexual spermatozoa, and they produce male sexual hormone, testosterone, which stimulates the hormone, testosterone, which stimulates the accessory male sexual organs and causes the accessory male sexual organs and causes the development of the masculine extragenital sex development of the masculine extragenital sex characteristics.characteristics.

The testis is surrounded by a thick capsule, the The testis is surrounded by a thick capsule, the tunica albugineatunica albuginea

300 lobuli testis =Each lobule contains 1-4 300 lobuli testis =Each lobule contains 1-4 convoluted seminiferous tubules (about 150-convoluted seminiferous tubules (about 150-300 µm in diameter, 30-80 cm long). 300 µm in diameter, 30-80 cm long).

The Convoluted Seminiferous Tubules The Convoluted Seminiferous Tubules The insides of the tubules are lined with seminiferous The insides of the tubules are lined with seminiferous

epithelium, which consists of two general types of cells: epithelium, which consists of two general types of cells: spermatogenic cells and Sertoli cells. spermatogenic cells and Sertoli cells.

1-Spermatogenic cells:1-Spermatogenic cells:Spermatogonia Spermatogonia Two types of spermatogonia can be distinguished in the Two types of spermatogonia can be distinguished in the

human seminiferous epithelium:human seminiferous epithelium:Type A spermatogonia have a rounded nucleus with very Type A spermatogonia have a rounded nucleus with very

fine chromatin grains.fine chromatin grains.Type B spermatogonia have rounded nuclei with Type B spermatogonia have rounded nuclei with

chromatin granules of variable size.chromatin granules of variable size. Primary spermatocytesPrimary spermatocytes Secondary spermatocytes, Secondary spermatocytes, Spermatids, Spermatids, Spermatozoa Spermatozoa

Sertoli cellsSertoli cells are far less numerous than the spermatogenic cells and are far less numerous than the spermatogenic cells and

are evenly distributed between them. Their shape is are evenly distributed between them. Their shape is highly irregular - columnar is the best approximationhighly irregular - columnar is the best approximation

Sertoli cells also secrete two hormonesSertoli cells also secrete two hormones - inhibin and - inhibin and activin - which provide positive and negative feedback activin - which provide positive and negative feedback on FSH secretion from the pituitary.on FSH secretion from the pituitary.

Interstitial tissueInterstitial tissue Leydig cellsLeydig cells (15-20 µm), (15-20 µm), located in the interstitial located in the interstitial

tissue between the convoluted seminiferous tubules, tissue between the convoluted seminiferous tubules, constitute the constitute the endocrine component of the testisendocrine component of the testis. . They They synthesise and secrete testosteronesynthesise and secrete testosterone. Ledig cells occur . Ledig cells occur in clusters , which are variable in size and richly in clusters , which are variable in size and richly supplied by capillaries. The cytoplasm is strongly supplied by capillaries. The cytoplasm is strongly acidophilic and finely granular. The nucleus is large, acidophilic and finely granular. The nucleus is large, round and often located eccentric in the cell.round and often located eccentric in the cell.

Female Reproductive SystemFemale Reproductive System

This section focusses on the internal This section focusses on the internal female reproductive organs:female reproductive organs:

1- 1- The ovaries, The ovaries,

2-Fallopian tube or oviducts, 2-Fallopian tube or oviducts,

3-Uterus 3-Uterus

4-Vagina. 4-Vagina.

5-Mammary gland5-Mammary gland

The OvariesThe Ovaries

The ovaries have two functions - The ovaries have two functions - "production" and ovulation of oocytes and "production" and ovulation of oocytes and the production and secretion of the production and secretion of hormones.hormones.

The surface of the ovary is covered by a The surface of the ovary is covered by a single layer of cuboidal epithelium, also single layer of cuboidal epithelium, also called called germinal epitheliumgerminal epithelium. .

Like so many other organs the ovary is Like so many other organs the ovary is divided into an outer divided into an outer cortexcortex and an inner and an inner medullamedulla. The cortex consists of a very . The cortex consists of a very cellular connective tissue stroma in which cellular connective tissue stroma in which the ovarian follicles are embedded. The the ovarian follicles are embedded. The medulla is composed of loose connective medulla is composed of loose connective tissue, which contains blood vessels and tissue, which contains blood vessels and nerves nerves

Ovarian FolliclesOvarian Follicles

Ovarian follicles consist of one oocyte Ovarian follicles consist of one oocyte and surrounding and surrounding follicular cellsfollicular cells. . Follicular development can be Follicular development can be divided into a number of stages.divided into a number of stages.

Primordial follicles Primordial follicles

are located in the cortex just beneath are located in the cortex just beneath tunica albuginea. One layer of flattened tunica albuginea. One layer of flattened follicular cells surround the oocyte (about follicular cells surround the oocyte (about 30 µm in diameter). The nucleus of the 30 µm in diameter). The nucleus of the oocyte is positioned eccentric in the cell. oocyte is positioned eccentric in the cell. It appears very light and contains a It appears very light and contains a prominent nucleolus.prominent nucleolus.

The primary follicleThe primary follicle • is the first morphological stage that marks is the first morphological stage that marks

the onset of follicular maturation the onset of follicular maturation

The previously flattened cell surrounding the The previously flattened cell surrounding the oocyte now form a cuboidal or columnar oocyte now form a cuboidal or columnar epithelium surrounding the oocyte. Their epithelium surrounding the oocyte. Their cytoplasm may have a granular appearance, cytoplasm may have a granular appearance, and they are for this reason also and they are for this reason also called called granulosa cells. And granulosa cells. And The The zona pellucidazona pellucida becomes visible.becomes visible.

The oocyte of the The oocyte of the secondary folliclesecondary follicle reaches a diameter of about 125 µm. reaches a diameter of about 125 µm. The follicle itself reaches a diameter The follicle itself reaches a diameter of about 10-15 mm. of about 10-15 mm.

The mature or tertiary or preovulatory or GraafianThe mature or tertiary or preovulatory or Graafian follicle follicle

increases further in size (in particular in the last increases further in size (in particular in the last 12h before ovulation). 12h before ovulation).

AtresiaAtresia

Atresia is the name for the degenerative Atresia is the name for the degenerative process by which oocytes (and follicles) process by which oocytes (and follicles) destroyed without having been eject by destroyed without having been eject by ovulation. Only about 400 oocytes ovulation. Only about 400 oocytes ovulate - about 99.9 % of the oocytes ovulate - about 99.9 % of the oocytes that where present at the time of puberty that where present at the time of puberty undergo atresia.undergo atresia.

By the sixth month of gestation about 7 By the sixth month of gestation about 7 million oocytes are present in the ovaries. million oocytes are present in the ovaries. By the time of birth this number is By the time of birth this number is reduced to about 2 million. Of these only reduced to about 2 million. Of these only about 400.000 survive until puberty. about 400.000 survive until puberty.

The Oviduct or fallopian tube The Oviduct or fallopian tube

The fallopian tube functions as a duct The fallopian tube functions as a duct for the oocyte, from the ovaries to the for the oocyte, from the ovaries to the uterus. Histologically, the fallopian tube uterus. Histologically, the fallopian tube consists of a consists of a mucosamucosa and a and a muscularismuscularis

The mucosa The mucosa is formed by a ciliated and secretory epithelium resting on a very cellular is formed by a ciliated and secretory epithelium resting on a very cellular

lamina propria. The number of ciliated cells and secretory cells varies lamina propria. The number of ciliated cells and secretory cells varies along the oviduct . Secretory activity varies during the menstrual along the oviduct . Secretory activity varies during the menstrual cycle, and resting secretory cells are also referred to as peg-cells.cycle, and resting secretory cells are also referred to as peg-cells.

The UterusThe Uterus

The uterus is divided into The uterus is divided into bodybody and and cervixcervix. . The walls of the uterus are composed of : The walls of the uterus are composed of : The The endometrium endometrium the the myometriummyometrium. . Endometrium Endometrium The endometrium consists of a simple columnar epithelium The endometrium consists of a simple columnar epithelium

(ciliated cells and secretory cells) and an underlying thick (ciliated cells and secretory cells) and an underlying thick connective tissue. The mucosa is folded to form many connective tissue. The mucosa is folded to form many simple tubular uterine glands.simple tubular uterine glands.

Myometrium Myometrium - The muscle fibres of the uterus. The muscle fibres of the uterus.