BIOL 252 Exam 4

What are excretory functions of the kidney?

filter blood and remove wastes, regulate osmolarity of fluids, regulate acid-base balance

What are cardiovascular functions of the kidney?

regulate blood volume and regulate blood pressure

What are endocrine functions of the kidney?

Releases EPO (stimulates RBC production), vitamin D (stimulates calcium uptake), and renin (regulates systemic BP and renal blood flow)

What is filtration in the kidney?

blood plasma (excluding proteins and cells) moves into tubules

What is reabsorption in the kidney?

solutes and water are transported out of the tubule, back into the peritubular capillaries

What is secretion in the kidney?

solutes are transported into the tubule, removing substances from the peritubular capillaries

What is urine?

the excreted product of remaining after filtration, reabsorption, and secretion

What is the function of the filtration membrane?

Keeps out large particles (proteins and larger), and about 20% of the blood plasma leaves the blood and becomes filtrate

What is the role of the proximal tubule?

a major site for reabsorption - has “brush border” to enhance surface area

Why is the net filtration pressure important?

The NFP explains why fluid moves into the capsular space, determines how much filtrate is produced over time (Glomerular filtration rate)

What is the juxtaglomerular apparatus?

if too little water or sodium (low BP), macula densa produces renin

the connection between distal tubule and efferent and afferent arterioles

What are the three forces that provide the Net Filtration Pressure?

Glomerular hydrostatic pressure, capsular hydrostatic pressure, colloid osmotic pressure

What is glomerular hydrostatic pressure?

Higher than other capillaries bc efferent arteriole diameter is lower than afferent arteriole diameter (promotes filtration/movement out of capillaries)

What is capsular hydrostatic pressure?

Higher than interstitial hydrostatic pressure bc promotes movement of water and solutes back into glomerular capillaries (slows down filtration)

What is colloid osmotic pressure?

Pressure that proteins in the glomerular capillaries exert to keep water from leaving the capillaries (counteracts hydrostatic pressure)

What is a normal GFR?

180 L/day

What is a normal urine output?

1-2 L/day

What are the mechanisms employed for the autoregulation of GFR?

myogenic mechanism (80-180 mmHg)

tubuloglomerular feedback

How does a kidney stone decrease NFP compared to normal?

When the flow of urine is blocked, capsular hydrostatic pressure increases bc fluid not effectively drained, opposing filtration

How does the myogenic mechanism auto-regulate GFR?

when BP low = afferent arteriole dilate = increase GFR

when BP high = afferent arteriole constrict = decrease GFR

What does the tubuloglomerular feedback system do?

when GFR high = filtrate in the tubule increases = NaCl in filtrate increases = macula densa (in distal tubule) detects high NaCl = MD releases ATP = afferent arteriole constricts = low GFR

What is the effect of the RAAS system on the GFR? (specifically JG cells)

decrease in systemic blood pressure is sensed by juxtaglomerular cells causing renin to be released, promoting the conversion of angiotensinogen to angiotensin-I.

This increases efferent arteriole constriction and eventually increases GFR and systemic blood pressure

What is the effect of the RAAS system on the GFR? (specifically angiotensin-II)

constricts efferent arterioles —> increases GFR

constricts systemic arterioles, increases thirst, increases Na+ reabsorption —> increases systemic blood pressure (in proximal tubules)

also stimulates aldosterone which increases systemic blood pressure by increasing Na+ reabsorption (in distal tubules)

What does ANP (atrial natriuretic peptide) do?

when BP is high and GFR is high = ANP causes either dilation of afferent or constriction of efferent arteriole = increase fluid loss

How does the sympathetic system stimulate the kidney/regulate GFR?

sympathetic stimulation of JG cells = renin is released by JG cells = angiotensin II is produced = constriction of efferent arteriole

note that NE (released due to sympathetic stimulation) can cause constriction of the afferent arteriole

How does Na+ reabsorption in the proximal tubule work?

using secondary active transport, Na+/glucose symporters moves both out of the filtrate

Na+/K+ ATPase pump (primary active transport) moves Na+ out of the cell and into the ISF

glucose is carried out through a facilitated diffusion transporter

What is the obligatory water reabsorption that occurs during Na+ reabsorption in the proximal tubule?

water follows Na+ reabsorption through aquaporins and other channels

What is secreted?

some wastes and H+

What is reabsorbed?

all nutrients, some salts and water, some HCO3-

What are the two roles of the Loop of Henle?

establishes the medullary osmolarity gradient, concentrates wastes

kidney has an osmolarity gradient within the interstitial fluid, too

How does countercurrent multiplication work?

Loop of Henle establishes the medullary concentration gradient by first transporting Na+ and Cl- to the interstitial fluid. This then draws water out of the filtrate, causing filtrate concentration to increase due to water loss. High filtrate concentration then increases salt transport to the ISF (more salt transported from bottom than top).

What do principal cells do in the distal convoluted tubule and collecting duct?

reabsorb Na+ and secrete K+

What do intercalated cells do in the distal convoluted tubule and collecting duct?

secrete H+

What are principal and intercalated cells activated by?

Aldosterone —> activated by low Na+, high K+, high H+

How is dilute urine formed?

When no ADH is present that means there is low blood osmolarity and high blood volume. thus, blood volume decreases = osmolarity increases and water is secreted into the kidneys

How is concentrated urine formed?

When ADH is present that means there is low blood volume and high blood osmolarity. This causes blood volume to increase = osmolarity deceases where aquaporins allow water to move through the collecting duct.

What do angiotensin II, aldosterone, and ADH do?

promote Na+ reabsorption

What does ANP do?

inhibits sodium ion reabsorption

What is dentin?

acellular, 70% inorganic matrix, produced by odontoblasts

What is enamel?

acellular, more than 95% inorganic matrix, produced by ameloblasts

Nervous and endocrine regulation of motility and secretion

stimuli: mechanical or chemical

response: secretory or contractile

Long reflexes: ANS

Short reflexes: ENS (hormones)

Which nutrient starts digestion in the mount, with the action of saliva?

Lipids and carbohydrates

What is peristalsis?

gradual movement of contents towards colon

circular smooth muscle contracts behind the bolus, longitudinal muscle contracts in front of the bolus (segment shortens and widens)

What is segmentation?

pinching off of a segment, followed by churning within the segment

What are the functions of the stomach?

storage; mechanical digestion; liquefies the bolus, producing chyme; chemical digestion of protein 

What is gastric motility?

the stomach controls its own motility, but may be influenced by the vagus nerve

the emetic center of the medulla can cause “reverse peristalsis” via the vagus nerve

What do parietal cells do?

They secrete H+ Cl- and intrinsic factor

What do chief cells do?

They secrete pepsinogen

What do endocrine cells do?

Also called G cells, they secrete gastrin, stimulating secretions from parietal cells

What are the three phases that regulate gastric secretion?

cephalic phase, gastric phase, intestinal phase

What does the duodenum do?

receives stomach contents, bile salts, pancreatic HCO3-, and enzymes

hormones regulate stomach, pancreas, and gall bladder activity: gastrin, secretin, CCK

stomach acid is neutralized here (pancreatic HCO3-)

enzymes begin chemical digstion (from the pancreas)

fats are physically broken up (bile acids from gall bladder)

What does the celiac phase do?

sight, smell, taste, and thoughts of food —> vagus nerve stimulation —> endocrine cells —> (increases gastrin, increases histamine, decreases somatostatin) —> stimulates parietal cells —> increases H+ release

What does the gastric phase do?

food entering stomach —> vagus nerve and enteric nervous system stimulation —> stimulates endocrine cells —> (increases gastrin, increases histamine, decreases somatostatin) —> increases H+ release

note: gastrin stimulates partially digested proteins in gastric juice which stimulates endocrine cells

What does the intestinal phase do?

declining pH and presence of lipids in duodenum stimulates enterogastric reflex which then stimulates vagus nerve activity and H+ secretion. Thus increases secretin and GIP, which inhibits parietal cell from releasing H+

What do acinar cells do?

Acinar cells produce a HCO3- rich aqueous solution and enzymes

What is secreted by pancreatic acinar cells?

proteases, lipase, amylase, ribonuclease, deoxyribonuclease, “pancreatic juice” (rich in HCO3-)

pancreatic zymogens (proenzymes) are converted to active enzymes in the duodenum

what are the functions of the liver?

1. hepatocytes

2. receive blood directly (oxygen delivered)

3. send out to the body: glucose, angiotensinogen, other plasma proteins

4. excrete into the bile: bile salts, cholesterol, bilirubin

What are the units of the liver?

Lobule

What are the functions of the gallbladder?

stores and concentrates bile:

• bilirubin - excretory product

• bile sallts (acids) - steroids synthesized from cholesterol

How much bile is released from the liver daily?

500-1000 mL

What percent of bile salts are reabsorbed in the small intestine?

80%

What does the stretch and macromolecules in the duodenum initiate for regulation of pancreatic secretions?

Parasympathetic stimulation in which ACh from vagus and enteric nerves stimulates enzymatic secretion

What do fats in the duodenum initiate for regulation of pancreatic secretions?

CCK release where CCK initiates pancreatic enzyme release and gall blader contraction

What does low pH in the duodenum initiate for regulation of pancreatic secretions?

secretin release into the blood which stimulates pancreatic release of bicarbonate

What does low pH in the duodenum initiate in the stomach?

secretin and CCK neural reflexes which inhibits secretion and motility (neg feedback)

How does carbohydrate digestion work?

salivary and pancreatic amylases break starch into disaccharides, trisaccharide, and branched oligosaccharides

How does carbohydrate absorption work?

after a final digestive step, monosaccharides are absorbed by intestinal epithelium

How does protein digestion and absorption work?

gastric pepsin and pancreatic proteases break proteins into oligosaccharides

What is the process of lipid digestion and absorption?

1. Lipids (triglycerides) are emulsified by bile salts

2. Small micelles are formed: tiny droplets covered in bile salts and lipases

3. Fatty acids, monoglycerides pass into intestinal cells

4. Triglycerides reassembled and packaged as a chylomicron that is exported from the cell

5. Chylomicrons enter the lacteal (lymphatic vessel)

What is the function of the large intestine?

Absorbs water and electrolytes (compaction)

What is the composition of feces?

water (3/4)

solids (1/4)

• 30% bacteria

• 30% undigested fiber

• 10-20% fat

• remaining: mucus and sloughed epithelial cells

What is bacterial flora?

500+ species of bacteria populate the large intestine

ferment undigested carbohydrates help in synthesis of certain vitamins

How is the iliocecal valve and colon regulated?

Gastroileal and gastrocolic reflex

What does the gastroileal reflex do?

relaxes iliocecal vale and increases peristalsis in ileum (allows movement from small to large intestine)

What does the gastrocolic reflex do?

food entering the stomach causes contraction of colon to make way for new food

stretching of stomach results in movement of luminal contents in the lower GI tract

What is the involuntary defecation reflex?

1. Visceral sensory neurons respond to stretch receptors

2. parasympathetic neurons cause contraction of sigmoid colon and rectum, relaxation of internal sphincter

How does voluntary defecation work?

relaxation of external sphincter (control)

What do seminiferous tubules do?

Contain sperm-forming cells

mature sperm are produced in the lumen, continuous with the male duct system (epididymis, vas deferens)

Made of sustentacular cells

What do interstitial cells do?

Produce testosterone

What do sustentacular cells do?

produce ABP and inhibin (testosterone regulation)

guide spermatogenesis

What does mitosis occur between in males?

Spermatogonium to primary spermatocyte

What does meiosis I occur between in males?

Primary spermatocyte to secondary spermatocyte

What does meiosis II occur between?

Secondary spermatocyte to Spermatid

What does spermiogenesis occur bewteen in males?

Spermatid to spermatozoa (sperm)

What does FSH stimulate?

Inhibin (negative feedback loop on FSH)

ABP (concentrates testosterone in sustentacular cells)

What does LH stimulate?

stimulates testosterone in interstitial cells of testes (negative feedback loop on GnRH)

What are the roles of testosterone?

onset and maintenance of spermatogenesis; growth/maturation of sex organs; growth of body hair and glands; body growth and male differentiation

What are aging’s effects on testosterone?

sustentacular and interstitial cells decline in number

testosterone declines

decrease in libido, body mass, self-confidence

What does testosterone cause in the beginning of childhood?

responsible for embryonic acquisition of male sex characteristics

What does testosterone cause during puberty?

In beginning causes onset of GnRH, FSH, and LH secretion

At end of puberty causes production of viable sperm

What does testosterone cause at end of adolescence?

adult stature

What is the result of oogenesis?

Diploid cell becomes haploid cells

cyclic hormonal changes result in the production of a single gamete per monthly cycle unlike males where all four gametes are mature sperm cells

Oogenesis during embryonic and fetal life

Oogonium undergoes mitosis where about 5 to 6 million oogonia are formed in the fetal ovary