Mcat Biology Lecture 6

Front 1

Digestive tract

Back 1

1. mouth
2. esophagus
3. stomach
4. small intestines (duodenum, ileum, jejunum)
5. large intestines (ascending colon, transverse colon, descending colon, sigmoid colon)
6. rectum
7. anus

Front 2

Mouth

Back 2

Digestion begins in the mouth with alpha-amylase contained in saliva

breakdown of starch

chewed food forms clump called bolus

Front 3

alpha-amylase

Back 3

contained in saliva

begins breakdown of starch (carbohydrates) into polysaccharides

Front 4

esophagus

Back 4

bolus is pushed into esophagus from mouth by swallowing

bolus is moved down esophagus by peristaltic action

saliva acts to lubricate esophagus to help food move down

no digestion occurs

Front 5

peristaltic action

Back 5

wave motion, similar to squeezing a tube of toothpaste at bottom and sliding fingers toward top to expel toothpaste

movement is performed by smooth muscles

Front 6

stomach

Back 6

bolus moves into stomach through lower esophageal sphincter (cardiac sphincter)

very flexible pouch that mixes and stores food

reduces bolus to semifluid mass called chyme

contains exocrine glands within its gastric pits

begins protein digestion with enzyme pepsin

low pH assists by denaturing proteins (pH 2) and kills bacteria

no absorption occurs

Front 7

4 major cell types of stomach

Back 7

1. mucous cell
2. chief (peptic) cell
3. parietal (oxyntic cells)
4. G cell

Front 8

G cell

Back 8

secrets gastrin into interstitium (bloodstream), which stimulates parietal cells to secrete HCl

Front 9

Mucous cell

Back 9

contains rough ER and golgi to make mucus, composed of glycoprotein and electrolytes

secretes mucus to lubricate stomach and protect epithelial lining

different types

line stomach wall and necks of exocrine glands

some secrete small amounts of pepsinogen

Front 10

parietal cell

Back 10

found in exocrine glands of stomach

secrete HCl, which diffuses to lumen. also secrete intrinsic factor, helps ileum absorb B12

used to lower pH of stomach and raise pH of blood

Have many mitochondria to produce sufficient energy to establish proton gradient

Front 11

Chief (peptic) cell

Back 11

synthesizes pepsinogen on rough ER, which is later cleaved to active pepsin

deep in exocrine glands

secret pepsinogen (zymogen precursor of pepsin)

Front 12

pepsinogen

Back 12

zymogen precursor to pepsin

activated to pepsin by low pH in stomach

once activated, pepsin beings protein digestion

Front 13

gastrin

Back 13

secreted by G cells into interstitium

large peptide hormone

absorbed into blood

stimulates parietal cells to secrete HCl

Front 14

Major hormones affects secretion of stomach juices?

Back 14

1. acetylcholine: increases secretion of all cell types

2. gastrin: increase secretion of HCl

3. histamine: increase secretion of HCl

Front 15

Small intestines

Back 15

90% of digestion and absorption occurs in small intestines

3m in length

divided into 3 parts (smallest to largest):
1. duodenum (digestion)
2. jejunum (absorption)
3. ileum (absorption)

Pyloric sphincter is between stomach and duodenum

Front 16

villi

Back 16

finger-like projections that covers outermost layer of small intestines

increases surface area, allowing for greater digestion and absorption

each contain capillary network and lymph vessel (lacteal) through which absorbed nutrients pass

Front 17

microvilli

Back 17

smaller finger-like projections on apical (lumen side) surface of cells of each villus (cells called enterocytes)

increase surface area

appear as fuzzy covering

Front 18

brush border

Back 18

fuzzy covering of microvilli on villus

contains membrane bound digestive enzymes for carbohydrates, proteins, nucleotides

Front 19

goblet cells

Back 19

epithelial cells on the small intestinal lining that secrete mucus to lubricate intestines and help protect brush border from mechanical and chemical damage

Front 20

Pancreas

Back 20

secretes bicarbonate ion into duodenum to make pH 6

exocrine glands

also secretes enzymes:
trypsin, chymotrypsin, pancreatic amylase, lipase, ribonuclease and deoxyribonuclease

all enzymes are released as zymogens

Enterokinase activates trypsin which activates other enzymes

Front 21

trypsin and chymotrypsin

Back 21

degrade proteins into small polypeptides.

Carboxypeptidase (pancreatic enzyme) further cleaves amino acids from the sides of the peptides

Front 22

pancreatic amylase

Back 22

like salivary alpha-amylase, but more powerful

digests starch, carbohydrates

hydrolyzes polysaccharides to disaccharides and trisaccharides

degrades carbohydrates of chyme to small glucose polymers

Front 23

lipase

Back 23

degrades fats, specifically triglycerides

since intestinal fluid is aqueous solution, fat clumps together, reducing surface area, which makes degradation difficult, problem fixed by addition of bile

Front 24

bile

Back 24

produced by liver and stored in gall bladder

gall bladder releases bile into small intestines

needed to increase surface area of fat

physically separates fat molecules, but does not chemically break down fat

emulsifies fat, doesn't digest fat

Bile is reabsorbed by small intestine and transported back to liver

Front 25

emulsification

Back 25

what bile does to fat

breaking up of fat into small particles without changing it chemically

increases surface area of fat, allowing lipase to degrade it into fatty acids and monoglycerides

Front 26

large intestines

Back 26

site of water and electrolyte absorption

profuse water loss, diarrhea, results when there is a problem with large intestines

mutualistic symbiosis between humans and bacteria (E. coli) in large intestines, bacteria get our leftovers and we get vitamins (K, B12, thiamin and riboflavin)

made up of:
1. ascending colon
2. transverse colon
3. descending colon
4. sigmoid colon

Front 27

glycogenesis

Back 27

formation of glycogen from glucose

glycogen is stored

occurs when blood glucose levels increase

occurs in liver and muscle cells

all cells are capable of storing glycogen, liver and muscle cells store most glycogen

Front 28

glycogenolysis

Back 28

occurs when blood glucose levels decrease

glycogen in converted to glucose

takes place in the liver and glucose is returned to blood

Front 29

urea

Back 29

ammonia is converted to urea by liver and then excreted in urine by kidney

Front 30

albumin

Back 30

fatty acids combine with albumin in the blood

single molecule of albumin carried 3 fatty acid molecules, but is capable of carrying up to 30

Front 31

the liver and the vena cava

Back 31

Vena cava is the location where all blood that has passed through liver is deposited

The liver receives blood from the capillary beds of the intestines, stomach, spleen, and pancreas via the hepatic portal vein.

Front 32

functions of liver

Back 32

1. blood storage
2. blood filtration (kupffer cells phagocytize bacteria)
3. carbohydrate metabolism (regulates blood glucose through gluconeogenesis, glycogenesis, storage of glycogen)
4. fat metabolism (cholesterol -> bile, carbs/protein -> fat, forms lipoproteins)
5. protein metabolism (forms urea from ammonia in blood, synthesizes plasma proteins, deaminates AA's, synthesizes NONessential AA's)
6. detoxification
7. erythrocyte destruction
8. vitamin storage (A, D, B12, ferritin)

when the liver mobilizes fat or protein for energy, the liver makes ketone bodies which increases blood acidity (acidosis)

Front 33

Kidney function

Back 33

1. excrete waste products (urea, uric acid, ammonia and phosphate)
2. maintain homeostasis of body fluid volume and solute composition
3. help control plasma pH

Front 34

Kidney

Back 34

2 fist-size organs

made up of:
1. outer cortex
2. inner medulla

The kidney creates urine

Front 35

What is the renal pelvis? What is the flow of urine starting from renal pelvis?

Back 35

Renal pelvis is where urine is emptied to from the kidney

Renal pelvis -> ureter -> bladder -> urethra

Front 36

nephron

Back 36

the functional unit of kidney

Made up of:
1. glomerulus
2. bowman's capsule
3. renal corpuscle
4. proximal tubule
5. loop of henle
6. distal tubule
7. collecting duct
8. juxtaglomerular apparatus

Front 37

glomerulus

Back 37

First step: blood flows into the 1st capillary bed of nephron

hydrostatic pressure forces some plasma through fenestrations of the glomerular endothelium and into Bowman's capsule. The glomerulus contains fenestrations which sieve out filtrate (primary urine) and hold back blood cells and large proteins.

Front 38

renal corpuscle

Back 38

made up by bowman's capsule and glomerulus

it is where filtration occurs

Front 39

proximal tubule

Back 39

After filtrate is sieved into bowman's capsule, the filtrate moves to the proximal tubule.

Proximal tubule is where most reabsorption takes place

secondary active transport proteins in apical membranes of proximal tubule cells are responsible for reabsorption of glucose, proteins and other solutes

water is reabsorbed across relatively permeable tight junctions due to favorable osmotic gradient

drugs, toxins and other solutes are secreted into filtrate by cells of proximal tubule

also secreted into proximal tubule:
uric acid, bile pigments, antibiotics and other drugs

Antiport system: secretes H+ ions into the filtrate through Na+, driven by Na+ concentration gradient. similar to transport system of glucose with Na+, except H+ crosses membrane in opposite direction to Na+

net result of proximal tubule:
reduce amount of filtrate in nephron, while changing solute composition without changing osmolarity

Front 40

loop of henle

Back 40

filtrate flows to here from proximal tubule

dips into medulla

It concentrates solute into the medulla, thus increasing osmotic pressure of medulla.

water passively diffuses out and into medulla

2 parts:
1. descending loop of henle
2. ascending loop of henle
The vasa recta is a second capillary bed that surrounds the loop of henle and helps to maintain the concentration of the medulla.

Front 41

descending loop of henle

Back 41

As filtrate descends into the medulla, water passively diffuses out of the loop of Henle and into the medulla.

DLOH has low permeability to salt, so filtrate osmolarity goes up.

DLOH is permeable to water

Front 42

ascending loop of henle

Back 42

As filtrate rises out of medulla into cortex, salt diffuses out, passively at first and then actively

ALOH is impermeable to water

actively transports Na+ into kidney

Front 43

distal tubule

Back 43

reabsorbs Na+ and Ca+2

secretes K+, H+ and HCO3-

ADH acts on distal tubule cells to increase Na+ & K+ membrane transport proteins

net effect of distal tubule:
lower filtrate osmolarity

ADH acts to increase permeability of cells to water

presence of ADH, water flow from tubule, concentrating filtrate

Front 44

collecting duct

Back 44

where distal tubules empties

carries filtrate into highly osmotic medulla

impermeable to water and sensitive to ADH

In the presence of ADH, collecting duct becomes permeable to water allowing it to passively diffuse in medulla, concentrating urine

leads to renal pelvis

Front 45

juxtaglomerular apparatus

Back 45

monitors filtrate pressure in distal tubule

granular cells secrete renin enzyme, to initiate regulatory cascade which ultimately stimulates adrenal cortex to secrete aldosterone

aldosterone acts on distal tubule, stimulating formation of membrane proteins that absorb Na+ and secrete K+

Front 46

Aldosterone

Back 46

Acts on the distal tubule. Stimulates the formation of membrane proteins that absorb sodium and secrete potassium. Raises blood pressure.

Renin -> angiotensin -> aldosterone