Test 4 Renal & Metabolism

What are the functions of the kidneys?

regulation of extracellular fluid and blood pressure

regulation of osmolarity

maintenance of ion balance

homeostatic regulation of pH

excretion of wastes

production of hormones

What is the functional unit of the kidney?

nephron

What are the two layers of the kidney?

outer cortex and inner medulla

What is the renal corpuscle?

site of plasma filtration that includes the Bowman’s capsule with the glomerulus

What is filtration?

fluid from blood into lumen of the nephron

occurs at renal corpuscle

dependant on pressure in capillaries

What is reabsorption?

materials in the filtrate are passed back into the blood

occurs with peritubular capillaries

may be active or passive

What is secretion?

active movement of material from blood into lumen to tubule

occurs with peritubular capillaries

active process that takes energy

important in homeostatic regulation

What is the process of the proximal tubule?

isosmotic reabsorption of organic nutrients, ions, and water; secretion of metabolites and xenobiotic molecules

What is the process of the loop of henle?

reabsorption of ions in excess of water to create dilute fluid in the lumen; countercurrent arrangements contribute to concentrated interstitial fluid in the renal medulla

What is the process of the distal nephron?

regulated reabsorption of ions and water for salt and water balance and pH homeostasis

What 3 pressures influence glomerular filtration?

capillary blood pressure (favors filtration)

capillary colloid osmotic pressure (opposes filtration)

capsule fluid pressure (opposes filtration)

What is glomerular filtration rate and what is it influenced by?

volume of fluid filtered per unit time

is relatively constant

controlled primarily by regulating blood flow through the renal arterioles

influenced by:

net filtration pressure

filtration coefficient

What decreases GFR?

increased resistance in afferent arteriole

decreased resistance in efferent arteriole

What increases GFR?

increased resistance in efferent arteriole

decreased resistance in afferent arteriole

What is a myogenic response?

intrinsic ability of vascular smooth muscle to respond to pressure changes

similar to autoregulation in other systemic arterioles

What is the tubuloglomerular feedback?

paracrine control

juxtaglomerular apparatus: macula densa cells detect NaCl in filtrate; granular cells secrete resin

What is transepithelial transport?

substances cross apical and basolateral membranes of the tubule epithelial cells

What is the paracellular pathway?

substances pass through the cell-cell junction between two adjacent cells

What are the components of active transport of sodium?

creates electrical gradient

anions follow sodium creates osmotic gradient

water follows leaving behind higher concentrations of cations

cations follow down concentration gradients

exchangers (NHE) and pumps (Na+-K+-ATPase)

What is secondary active transport?

symport with sodium

moves glucose, amino acids, and other organic molecules with sodium

some transporters use H+ instead of Na+

What is passive reabsorption?

moves by diffusion following gradients created by Na+ active transport

What is endocytosis?

plasma proteins

receptor-mediated

digested by lysosomes

amino acids returned to circulation

What is saturation?

maximum rate of transport that occurs when all carriers are occupied by substrate

What is the transport maximum?

the transport rate at saturation

What is the renal threshold?

the plasma concentration at which a substance first appears in the urine

What is glucosuria or glycosuria?

glucose in urine

How do you calculate excretion?

filtration-reabsorption

What is clearance?

noninvasive way to measure GFR

what body actually does with material in tubules

rate at which a solute disappears from the body by excretion or by metabolism

What is micturition?

process of urination

What is the simple spinal reflex for urination?

stretch receptors in bladder walls send signal to spinal cord

parasympathetic fibers to induce bladder smooth muscle contraction and open internal sphincter

somatic neurons to external sphincter are inhibited

can be overridden by brainstem and cortex

What are the routes for excreting ions and water?

kidneys

some lost in feces and sweat

lungs lose water and bicarbonate

What is the behavior response primarily responsible for water gain in the body?

thirst and salt cravings

What is the response to decreased blood pressure and volume?

volume and baroreceptors trigger homeostatic reflexes

cardiovascular system increases cardiac output and vasoconstriction which helps increase blood pressure

thirst increases which should increase water intake which then increases ECF and ICF volumes which helps increase blood pressure

the kidneys conserve water and salt to help minimize further volume loss

What is the response to elevated blood pressure and volume?

volume receptors, endocrine cells, and baroreceptors trigger homeostatic reflexes

cardiovascular system decreases cardiac output and vasodilation which decreases blood pressure

kidneys excrete salts and water in urine which decreases ECF and ICF volume which helps decrease blood pressure

What are some ways we intake water?

ingestion, normal metabolism, IV

What are some ways we lose water?

urine, feces, insensible water loss (skin and exhalation), pathological (diarrhea, vomiting, excessive sweating)

What is the rapid response to maintain blood volume in the body? What is the slow response

respiratory and cardiovascular (rapid)

kidneys (slow)

What does the osmolarity of the urine represent?

how much water is excreted in the urine

low=high water

high=low water

What is diuresis?

removing excess water in urine

Why is the fluid leaving the Loop of Henle more dilute than fluid entering?

fluid travels based on concentration

loses water by osmosis to the medulla

cells in thick portion of ascending limb are impermeable to water and actively transport Na+ out of lumen into medulla

What is vasopressin?

antidiuretic hormone; prevents water from leaving body

acts on collecting ducts only

stimulated aquaporin insertion into the apical membrane with membrane cycling

exhibits circadian pattern so less urine is produced at night

activated by osmoreceptors that are stimulated by blood volume and osmolarity

What is the renal countercurrent multipler?

Loop of Henle transfers solutes by active transport into medulla, resulting in greater ECF osmolarities; vasa recta removes water

What is the homeostatic response to salt ingestion?

there is no change in volume but an increase in osmolarity

vasopressin is secreted which increases renal water reabsorption and then the kidneys conserve water

thirst response is activated which increases water intake which increases renal water reabsorption which increases ECF volume (causing kidneys to excrete salt and water) and blood pressure (cardiovascular reflexes lower blood pressure)

osmolarity, volume, and blood pressure return to normal

What is the renin-angiotensin pathway?

juxtaglomerular cells secrete the enzyme renin if blood pressure decreases

renin converts angiotensinogen to angiotensin I (does nothing in body)

angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II

stimulated by granular cells that are sensitive to blood pressure, sympathetic stimulation from cardiovascular center, paracrine feedback from macula densa cells

What does aldosterone do?

controls sodium balance

is a steroid hormone produced in adrenal cortex

reabsorption of Na+ (and K+ secretion) in distal tubules and collecting ducts

target principal cells increase opening time of ENaC and ROMK channels and increase activity of Na+-K+-ATPase

low blood pressure stimulates aldosterone secretion

high extracellular K+ stimulates adrenal cortex

shut off by very high osmolarity

What does angiotensin II do?

stimulated adrenal cortex to produce aldosterone

increases blood pressure by increasing vasopressin secretion, stimulating thirst, vasoconstricting, increasing sympathetic output to the heart and blood vessels, increasing proximal tubule Na+ reabsorption

What is natriuresis?

urinary loss of Na+

decreases blood volume by increasing GFR, decreases Na+ reabsorption, suppresses RAS

atrial natriuretic peptide

produced in atrial myocardial cells

brain natriuretic peptide

produced in ventricular myocardial cells and certain brain neurons

What is hypokalemia

muscle weakness and failure of respiratory muscles and the heart

What is hyperkalemia

too much potassium makes body excited and things fire when they aren’t supposed to

can lead to cardiac arrhythmias

What is the salt appetite?

craving for salty foods when plasma Na+ levels drop

What is the homeostatic compensation for severe dehydration?

cardiovascular mechanisms provide quickest response (decrease parasympathetic, increase sympathetic, arterioles constrict and increase resistance increasing blood pressure, heart rate and force increase increasing cardiac output, increases volume)

renin-angiotensin system (granular cells stimulate resin to convert angiotensinogen to ANG I, ACE converts to ANG II which stimulates adrenal cortex to decrease aldosterone and Na+ reabsorption which decreases osmolarity)

renal mechanisms (decrease GFR so volume conserved)

hypothalamic mechanisms (increase vasopressin and thirst, increases water reabsorption and intake, increases osmolarity and volume)

What can pH changes do to proteins?

denature

change 3-D structure

acidosis

neurons become less excitable, CNS depression

alkalosis

neurons become hyperexcitable; severe can lead to muscle tetanus

What are some types of acid input?

organic acids (diet and intermediates), metabolic organic acid production increase, ketoacids, production of CO2

What are some types of base input?

few dietary and metabolic sources

ex. Tums

What are some pH buffer systems?

proteins, phosphate ions, bicarbonate

create moderate changes by combining with or releasing H+

ventilation can compensate (corrects 75% but can also cause them)

kidneys use ammonia and phosphate buffers

What are some ways to remove acids from interstitial fluid?

apical Na+-H+ exchanger (NHE)

Na+-HCO3- symporter

H+-ATPase

H+-K+-ATPase

Na+-NH4+ antiport

What are some ways to add acids back into the interstitial fluid?

basolateral Na+-HCO3- symport

HCO3-Cl- antiport

What are type A intercalated cells associated with?

function in acidosis

H+ excreted, HCO3- and K+ reabsorbed

What are type B intercalated cells associated with?

function in alkalosis

HCO3- and K+ excreted, H+ reabsorbed

respiratory acidosis

caused by hypoventilation which increases CO2 which decreases pH

metabolic acidosis

dietary and metabolic input of H+ exceeds excretion, pH decreases, can be compensated for by hyperventilation

respiratory alkalosis

caused by hyperventilation which decreases CO2 which increases pH

metabolic alkalosis

loss of H+ through excessive vomiting or excessive ingestion of antacids which increases pH, can be compensated for by hypoventilation

What is the gut?

stomach through anus

primarily involved in digestion

What is chyme?

mixture of food and secretions

What are the 4 layers of the GI tract wall?

mucosa, submucosa (middle layer), muscularis externa (outer wall), serosa (outer covering)

What are the 4 basic processes of the GI tract?

digestion, absorption, secretion, motility

What are the 3 challenges of the GI tract?

avoiding autodigestion, mass balance, defense

What are the 2 purposes of motility?

moving food through the tract and mechanically mixing food to break it into uniformly small particles

What is motility?

GI smooth muscles contracting spontaneously

tonic contractions

last minutes or hours, hold unless signal comes in to open sphincter)

phasic contractions

last seconds, quick, on-off

What are the 3 patterns of contraction?

migrating motor complex, peristalsis, segmental contractions

What is the enteric nervous system?

independent nervous system of GI tract, controls motlity, secretion, growth

where short reflexes integrate

long reflexes integrate in CNS

What is the cephalic phase/reflex?

smelling, seeing, or thinking about food

reflex begins in brain

anticipation of/or presence of food in oral cavity activated neurons in medulla

mouth

where chemical and mechanical digestion begin

salivary secretions (soften and lubricate food, digestion starch, taste, defense)

mastication (chewing)

What are the 3 functions of the stomach?

storage, digestion, defense

How does the stomach protect itself from autodigestion?

mucus-bicarbonate barrier

intestine

motility: segmental and peristaltic

complete digestive process and allow for absorption

absorbed nutrients go to hepatic portal system to be filtered before entering bloodstream

fats go to lymphatic circulation to get to circulatory system

What are the 6 intestinal secretions?

digestive enzymes, bile, bicarbonate, mucus, isotonic NaCl secretion

What do the endocrine/islets of the pancreas secrete?

insulin and glucagon

What do the exocrine portion of the pancreas secrete?

digestive enzymes (acini) and sodium bicarbonate

brush border converts trypsinogen to trypsin

bicarbonate secretion to neutralize gastric acid

What is bile?

secreted by liver hepatocytes

composed of bile salts, bile pigments, cholesterol

aids in fat digestion

stored and concentrated in gallbladder

gallbladder send to duodenum through common bile duct

small intestine

where most digestion occurs

bile salts facilitate fat digestion

carbohydrates absorbed as monosaccharides

proteins

digested into small peptides and amino acids by two groups of enzymes (endopeptidases and exopeptidases)

peptide absorption

mostly amino acids

easier to bring in smaller things

some larger peptides can absorbed intact

endopeptidases

cleave in middle of long protein chains

exopeptidases

work on end of peptide chain

nucleic acids

digested into bases and monosaccharides

large intestine

concentrates waste

segmental contraction continues to mix chyme

mass movement moves chyme forward and triggers defecation

bacteria breakdown lots of undigested materials

lipophilic materials are absorbed

gastrocolic reflex

stomach fills, tells intestine to get rid of stuff to make more room

ex. why you may need to defecate right after a large meal

What 2 control centers does the hypothalamus control?

feeding center (usually in charge) vs. satiety center

total body energy

energy stored + energy intake + energy output

energy output

work + heat

What are the 3 categories of work done by our cells?

transport work, mechanical work, chemical work

most of this work is unconscious

direct calorimetry

measures energy content of food in kilocalories

metabolic energy slightly less because food is not fully digested