Subject code: HSP102 Human Structure & Physiology

Human Structure & Physiology

Dr. Vinicius CruzatSenior Lecturer and Research Fellow

Subject code: HSP102

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Concept 1Structure and function of the small

intestine

Human Structure & PhysiologySubject code: HSP102

Gastrin

Secretin

MotilinCCK

GIP (Gastric inhibitory polypeptide)

Widmaier et al., 2018.

Small intestine

Tortora & Derrickson, 2018.

Ø Intestinal juice provides a vehicle for absorption of substances from chyme as they come in contact with the villi

Ø Brush border enzymes, found on the surfaces of the microvilli of absorptive cells, break down food products

Small intestine


Two zones:a) surface or luminal zone (villi)b) Crypt or deep zone

Small intestine

46,800xTEM

Small intestine

Villi

Microvilli


Gastrointestinal (GI) Tract



IleumShort and digit form villi

Ø Absence of Brunner's

gland

Ø Prominent presence of

Peyer’s patches (or

aggregated lymphoid

nodules – secrete IgA)

Ø Presence of Paneth cells

at the base of the

Lieberkühn Crypts

JejunumLong and digit form villi

Ø Presence of Paneth cells

in the base of the Crypts

of Lieberkühn

(Lysosomes)

Ø Some presence of Paneth

cells in the lamina propria

layer

DuodenumLong and short villi

Ø Brunner's gland -

Submucosa (HCO3

secretion – pH control)

Ø Sphincter of Oddi (Larger

papillary - bile duct -

Pancreatic and Biliary

secretions)

Secondary Lymphatic Organs - GALT

Histological differences between duodenum, jejunum and ileum


Overall function - absorption in the Small IntestineSmall intestine


Concept 2Structure and function of the large

intestine


Large intestineThe last stages of digestion and absorption in the bodyØ Substances are further broken down by bacteria and some vitamins are

synthesized by bacterial actionØ Colon - tube that extends from the ileocecal part to the anus part of the gutØ Average measurment - about 125-150 cmØ Form - Inverted U shapeØ Width - about 6.5 cm diameter

Ileocecal valve - Prevents retrograde flow of fecal contents of the colon into the small intestine. Its a very thick muscular layer.


15cm 45cm

25cm

38cm

Houston valves (circular muscle fibre layer)

Without peritoneum, direct contact with left kidney.

Large intestine


Large intestine


Large intestineØ Haustral churning

Distension reaches a certain point and the walls of the haustra contract to squeeze contents onward

Ø PeristalsisPropulsive contractions

Ø Mass peristalsisA strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the rectum


Large intestineFeces formationConsist of water, inorganic salts, sloughed-off epithelial cells, bacteria, products of bacterial decomposition, and undigested portions of food



Brown stool type of colour = Pigment present in bile(brown stool coloration) destruction of ’old’ haemoglobin.

Large intestineDefecation reflex

1. Rectal wall distends2. Stretch receptors send sensory

nerve impulses to the sacral spinal cord

3. Motor impulses travel back to the descending colon, sigmoid colon, rectum, and anus

4. Longitudinal rectal muscles contract and the internal anal sphincter opens

If the external anal sphincter is voluntarily relaxed, defecation occurs and the feces are expelledTortora & Derrickson, 2018.

Wani & Thakur, 2016

Medical aid designed to classify the feces forms into 7 groups. Developed by Heatonand Lewis (University of Bristol, England), first published in 1997. Because the formof the stool depends on the time it spends in the colon, there is a correlationbetween the colonic transit time and the stool type.

5-7 tending towards diarrhea; dietary or

supplemental fiber can help regulate the form

of fecal waste.

The Bristol Stool Scale Types 1-2 = constipation

3 and 4 = "ideal stools" especially the 4 (easiest to pass)

Ø The appendix seems to have no function, however bacteria can proliferate inthis place which is part of the intestinal metabolism and serve as a stimulus forthe Immune system.

Ø Obstruction and inflammation in theappendix (appendicitis).Ø The faecal mass stimulates theinflammatory response, leading toappendicitis.

Large intestineAppendix


Concept 3Integration and absorption


Splanchnic circulation

Absorption



Absorption

a) Na-Glucose Co-transporters (SGLTs)

Special transport processes bind to glucose,fructose and galactose, allowing it to cross thephospholipid bilayer.

2 families are described

b) Facilitated diffusion glucose transporters (GLUTs)

Glucose transport


a) Na-Glucose Co-transporters (SGLTs) or secondary active transport

SGLT-1

Substance is transported against the electrochemical gradient, taking advantageof the "energetic ride" of another substance (Na+) that is transported in favour ofits gradient, both transported in the same direction.ü Transport of glucose and galactoseü Symport system (2 substances same direction)ü Secondary active transport 3Na+/2K+ ATPase in the basolateral membraneü Carries glucose against its concentration gradientü Saturation: 30-50 mM glucoseü Induced by CKK and GLP-2


Ø Has a specific combining site for the molecule being transported. Affinity for glucose, galactose and fructose

Ø "There is no ATP consumption by the cell" Transport depends on the extracellular [ ]Ø Substance moves according to the concentration gradient, > [ ] where << [ ]Ø Carry 35 mole of water / SGLT 210 mols

Kellett & Brot-Laroche, 2005.

Protein/Amino acid transport

Amino acid Peptides1) PepT-12) Transcellular movement pathway through direct peptide penetration and

endocytosis3) Paracellular movement


Free amino acids1) Specific amino acid

transporters

Broer, 2008.


Lipid transport

Lipid transport

A micelle is a sphere that formswhen the hydrophilic (water friendly)heads of phospholipids align to shieldhydrophobic fatty tails from thewatery environment.Vadakayil, 2010.

Lipid transport Chylomicron

Micelles

Minerals and water transport

The type and concentration ofsolute in a compartment determinesthe distribution of fluid in the othercompartments. In an equilibriumsituation, all compartments of theorganism have equal tonicity(osmolality) ~ 285 mOsmoles.


Intracellular Extracellular

Interstitial fluid Plasma/blood

Mg++K+ Na+

HPO42-

Na+K+

Cl- Cl-

Na+

Prot -

K+

Cl- Mg++ Mg++

Ca2+ Ca2+ Ca2+ HCO3-HCO3

-HCO3-

Prot -Prot - HPO42- HPO4

2-

Plas

ma

Plas

ma

Plas

ma

Intracellular liquid

Extracellular liquid

Differences in osmolality changes H2O movement between the extra and intracellular fluids/space

↓ osmolality in the extracellular space (e.g. hyper hydration) = H2O move from the extra to the intracellular space, to equal the osmolality and cause swelling.

Similar [ ] on both sides (extracellular and

intracellular space) the osmolality will the the same.

↑ osmolality in the extracellular (e.g. dehydration) = H2O move from intra to the

extracellular space, to equal the osmolality and cause cell

dehydration.

Aquaporin increases the rate of osmosis.

Aquaporins

The function of Aquaporin is to allow the passive diffusion of water across the cell membrane. The structure of Aquaporin is a donut and water goes through the donut hole.


”For a while scientists noticed the same thing. Water clearly efficiently enters a cell, but how?”

High H2O potentialLow solute concentration

Aquaporin protein makes a water channel through the cell (plasma) membrane.

Peter AgreJohns Hopkins

Roderick MacKinnon

Rockefeller

• Aquaporins are channel proteins that move water rapidly into the cell through facilitated diffusion.• They were discovered by these two in 1991.• They shared the 2003 Nobel Prize in Chemistry.

AquaporinsMinerals and water transport

Overviews and Animations for the Digestive System

http://www.wiley.com/college/interactions/Energy/content/Energy/dig3a/frameset2.htm

Ø Carbohydrate Digestion and Absorption


Ø Protein Digestion and Absorption


Ø Lipid Digestion and Absorption


Ø Hormonal Control of Digestive Activities









Main and recommended referencesØ Tortora, G. and Derrickson, B. (2014). Principles of Anatomy & Physiology. 14th ed. John Wiley & Sons.

Ø Tortora, G. and Derrickson, B. (2018). Principles of Anatomy & Physiology. 2th ed. Asia-Pacific EditionHybrid. John Wiley & Sons.

Ø Hall, J. E., & Guyton, A. C. (2015). Guyton and Hall textbook of medical physiology. 13th ed.Philadelphia, PA: Saunders Elsevier.

Ø McArdle, W. D., Katch, F. I., & Katch, V. L. (2014). Exercise physiology: Energy, nutrition, and humanperformance. 8th ed. Philadelphia: Lippincott Williams & Wilkins.

Ø Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2002). Molecular biology of thecell. 15th ed. New York: Garland Science.

Ø Abbas, A. K., Lichtman, A. H., & Pillai, S. (2017). Cellular and molecular immunology. 9th ed.Philadelphia: Saunders/Elsevier.

Ø Netter, F. H. (2018). Atlas of human anatomy. 7th ed. Philadelphia, PA: Saunders/Elsevier.

Ø Widmaier, Eric P., Raff, Hershel, Strang, Kevin T. (2018). Vander's human physiology: the mechanismsof body function 15th ed. Boston: McGraw-Hill Higher Education.

Ø Silverthorn, D. U. (2018). Human physiology: An integrated approach. 8th ed. San Francisco: Harlow:Benjamin Cummings.

Ø Boron, W. F., Boulpaep, E. L. (2016). Medical physiology: a cellular and molecular approach. 3rd ed.Philadelphia: Saunders/Elsevier.

Subject code: HSP102 Human Structure & Physiology

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