Lecture 18: Nutrition/Digestion/Urinary

Covers Chapters 34 & 35

What nutrients do animals need?*

• Nutrients that provide energy:– Carbohydrates– Lipids– Proteins

• Other nutrients– Minerals– Vitamins– Water

Carbs provide energy

• Carbs broken down into glucose for cellular respiration, makes ATP

• Glucose that is not needed at time of ingestion and breakdown is stored as glycogen in liver and muscle

• We can only store 1 day’s worth of glycogen, so any excess glucose left after all possible glycogen has been created is stored as fat.

Fats/oils can also provide energy

• *Most concentrated energy source• *More than TWICE as many Calories by weight

as carbs or proteins (need less of it to get same amount of Calories)

• *9 Calories per gram (fats), 4 calories per gram (carbs & proteins)

• Fats/oils can be broken down into fatty acids (monomers) which can enter cell respiration and also make ATP

Proteins

• Broken down into individual AA’s• AA’s used to make new proteins for the body

(structural proteins, enzymes, transport molecules and cell membranes)

• If carbs and fats are not available, AA’s from ingested protein can enter cell respiration to make ATP. In extreme starvation, protein from muscle tissue will break itself down into AA’s for cell respiration. (muscle-wasting)

Vitamins• Organic molecules needed in small amounts for

normal cell function, growth and development.• Many vitamins are required for proper function of

enzymes that control metabolic reactions in the body*– Fat-soluble: A, D, E, K

• A used to make light-capturing molecule rhodopsin• D required for normal bone formation• K required for blood clotting

– Water-soluble: C, B. Most act as coenzymes, working with enzymes to promote reactions that supply energy or synthesize biological molecules

• Vit B-1 is part of a coenzyme that converts pyruvate to acetyl Co-A• Vit B-2 is part of FAD+

Minerals

• Elements that play important roles in nutrition• Calcium, magnesium, phosphorus are major

constituents of bone and teeth• Sodium, potassium and calcium needed for

muscle contraction and conduction of nerve impulses

• Iron is a component of hemoglobin• Iodine found in thyroid hormones

Water

• All metabolic reactions occur in a “watery” atmosphere (cytoplasm, blood, etc)

• Water contributes to blood, saliva, lymph, and cytoplasm, urine

• Needed to carry nutrients, eliminate wastes

Evolution

• Humans evolved to eat whenever possible because food was not always be readily available

• Today, most humans eat more than they need• Store excess carbs and fat as body fat.

Calorie

• Amount of energy needed to raise 1 gram of water by 1 degree celsius

• Food calorie content is measured in units of 1,000 calories, also known as Calories

• Humans burn 70 Calories per hour at rest• Humans burn up to 20 Calories PER MINUTE

while working out• People differ in their metabolic rate: speed at

which reactions that release energy occur

How does digestion occur?*

• Ingestion: food brought in• Mechanical digestion: food is physically

broken down (larger surface area)• Chemical digestion: digestive chemicals and

enzymes break down food molecules into small subunits (monomers)

• Absorption: monomers transported out of digestive tract into the blood

• Elimination: indigestible material is eliminated

The Human Digestive Tract

Fig. 34-12

Oral cavity, tongue, teeth:

Stomach: Breaks down food and begins protein digestion

Small intestine: Food is digested and absorbed

Rectum: Stores

Salivary glands: Secrete lubricating fluid and starch-digesting enzymes

Pharynx: Shared digestive and respiratory passage

Epiglottis: Directs food down the esophagus

Esophagus: Transports food to the stomach

Liver: Secretes bile (also has many non-digestive functions)

Gallbladder: Stores bile from the liver

Pancreas: Secretes pH buffers and severaldigestive enzymes

Large intestine: Absorbs vitamins, minerals, and water; houses bacteria; produces feces

How do humans digest food? mouth to stomach*

• Ingestion• Mechanical Digestion: teeth break down food• Chemical Digestion: Three salivary glands produce

saliva: • Contains enzymes which begin to breakdown carbs (chemical

digestion)• Contain bacteria-killing enzymes and antibodies• Lubricate food• Some molecules dissolved and tongue identifies taste

• We swallow food: pharynx >> epiglottis >> esophagus>>stomach (propelled to stomach via peristalsis)

How do humans digest food? Stomach*

• Food enters stomach (muscular sac)• Sphincter muscles prevent regurgitation to esophagus and regulates exit

of food into small intestine• Mechanical Digestion: Churning contractions• Chemical Digestion: Secretions from gastric glands breakdown proteins

• Mucus: coats stomach to protect it from acidic environment• Hydrochloric acid: pH of 1-3, destroys microbes• Pepsinogen: converted to pepsin when in contact with HCL, pepsin

breaks proteins down into short chains of AA’s • Other important events:

– Hormone gastrin regulates digestion– Food now called CHYME– Peristaltic waves propel chyme to small intestine

How do humans digest food? Small Intestine*

• Food enters small intestine • Chemical Digestion: enzymes and other digestive

secretions from 3 sources digest/absorb food• Liver: makes bile, which dissolves ingested fats into microscopic

particles• Pancreas : secretes pancreatic juice, which contains enzymes:

amylase (carbs), lipase (fats), proteases (proteins)• Cells lining small intestine: secrete yet more enzymes

• Absorption: Small intestine is 8-10 feet long with numerous folds and projections (villi and microvilli) giving it a surface area 600 times larger than if it was a smooth tube (total 2700 square feet!)

How do humans digest food? Small Intestine*

• Absorption: Each villus is provided with rich supply of capillaries and a lymph capillary (lacteal). All of the following are absorbed:– Water (via osmosis)– Monosaccharides– Amino acids and short peptides– Fatty acids: absorbed, flow through lymphatic

system to be dumped into blood– Vitamins & minerals

The Structure of the Small Intestine

Fig. 34-16

villi

capillaries

arteriolelymphvesselvenule

lacteal

microvilli

intestinal gland

fold of the intestinal lining

(a) Small intestine (b) A fold of theintestinal lining

(c) A villus (d) Cells of a villus

How do humans digest food?Large Intestine

• 5 feet long in humans• Colon>>rectum>>anus• Indigestible cellulose from fruits and

vegetables, other unabsorbed nutrients and water enter from the small intestine*

• Flourishing colonies of bacteria use the waste to thrive and MAKE vitamins B and K

• Any remaining material compacted into feces

Hormonal control of digestion

• As food enters and moves through system, it stimulates production of:– Gastrin: released INTO BLOODSTREAM in response to

digested proteins in the stomach. It stimulates more acid secretion in stomach…gastrin production slows as pH in stomach lowers

– Secretin & Cholecystekinin: released by duodenum, and increase bile and pancreatic juice secretion and regulates the speed at which chyme moves through small intestine

Basic functions of human urinary system*

• Filtration of blood, removing water and small dissolved substances (including ions and nutrients like AA’s and glucose) and waste

• Selective reabsorption of nutrients and water (back into the blood)

• Secretion of excess water, drugs, excess ions and dissolved wastes (into the urine)

• Concentration of urine• What wastes? A byproduct of protein breakdown is

ammonia (NH3). It is toxic to humans. Liver changes it to urea (less toxic) Kidneys remove this from the body.

Urine Formation and Concentration

Fig. 35-6

1

Tubular secretion:Additional wastes areactively transported into the proximal and distaltubules from the blood

3

4

Filtration: Water, nutrients, and wastes are filtered from theglomerular capillaries into theBowman’s capsule of the nephron

Tubular reabsorption: In theproximal tubule, most water and nutrientsare reabsorbed into the blood

2

Concentration: The loop ofHenle produces a salt concentrationgradient in the extracellular fluid;in the collecting duct, urine maybecome more concentrated than theblood as water leaves by osmosis

bloodleaving theglomerulus

loop ofHenle

blood enteringthe glomerulus

Bowman’scapsule

collectingduct

distal tubule

proximaltubule

Urea Formation and Excretion

Fig. 35-2

ammonia NH3

amino acid

Proteins in food are digested

Amino acids are carried inthe blood to body cells

The cells convert the amino groups (-NH2) toammonia, which is carriedin the blood to the liver

1

2

3

urea

The liver converts ammoniato urea, which is less toxic

In kidney nephrons, ureais filtered into the urine

Urea is carried in the bloodto the kidneys

4

6

5

Urinary System Maintains Homeostasis*

• Regulating levels of sodium, potassium, chloride and calcium

• Maintaining proper pH of the blood by regulating hydrogen and bicarbonate ion concentrations

• Regulating water content in the blood• Retaining important nutrients such as glucose and

amino acids• Eliminating cellular waste products like urea• Secreting substances that regulate blood pressure

and blood oxygen levels (HORMONES)

Structures of human urinary system*

• Kidney: paired organs just above the waist, on either side of spinal column. Blood is filtered and urine is produced

• Ureters: carry urine to bladder• Bladder: temporary storage of urine• Urethra: tube carrying urine out of body

Urinary System

Kidney in more detail

• Blood supply from Renal Artery: nearly 1 quart per minute

• Capillaries bring blood to nephron, then surround nephron, making bloodstream available for more absorption

• Three parts to the kidney:– Cortex: outer layer– Medulla: inner layer– Pelvis: branched, funnel-like chamber that collects

urine and sends it to bladder

Kidney in Detail

Nephron: Functional unit of kidney*– Bowman’s capsule: blood from renal artery/capillary

enters here: filtration– Proximal convoluted tubule: reabsorption of ions, water

& nutrients, secretion of more waste and drugs from blood into tubule

– Loop of Henle: reabsorption of water and ions• The extracellular fluid concentration in the medulla is

high…this forces more water to be absorbed)– Distal convoluted tubule:reabsorption of ions, secretion of

drugs and excess ions– Collecting duct and tubule: reabsorption of H20 – final concentrated form of urine moves through ureter to

bladder where it is stored until we urinate

collecting duct

distal tubule

proximal tubule

glomerulus

Bowman’scapsule

arterioles

venule

branch of therenal vein

branch ofthe renalartery

loop of Henle

capillaries

An Individual Nephron and Its Blood Supply

Fig. 35-5

Fig. E35-2

FILTRATIONTUBULAR REABSORPTION& TUBULAR SECRETION

URINECONCENTRATION

renal cortex

renal medulla

osmosis

diffusion

active transport

Bowman’scapsule

loop of Henle

proximaltubule

distaltubule

1

2

3

4

5

67

8

H2O*H2O

H2O*

H2O*H2O

H2O

H2O

H2O

NaCIurea

NaCI

NaCI

NaCI

H+

NH3

somedrugs

Na+

nutrients

HCO3–

Ca2+

Cl–

K+

collecting duct

H+

K+

somedrugs

(extracellular fluid)

NaClCa2+

Hormonal control of kidneys: renin-angiotensin

• Kidneys release renin in response to low BP• Renin catalyzes formation of angiotensin in

bloodstream• Angiotensin

– Stimulates proximal tubules to reabsorb more Na+, and water follows

– Stimulates ADH release from pituitary: increases H2O absorption from collecting duct/tubule

– Causes artierioles throughout the body to constrict, increasing blood pressure

Hormonal control of kidneys:erythropoetin

• Released by kidneys when blood oxygen is low• Stimulates bone marrow to make more RBC’s• More RBC’s can carry more O2• Blood oxygen level up

Hormonal control of kidneys: Vasopressin/Anti-Diuretic Hormone

• Secreted by pituitary gland and carried in bloodstream to kidney

• It causes the increased production of aquaporins (channel proteins that reabsorb water) therefore allowing more H20 to be reabsorbed to the blood.

• If blood osmolarity (amount of solids/liquids) goes up, more ADH is released and more water reabsorbed to keep blood diluted