Topic 8 (Part II) - Kidney Structure and Function

What specialized tubules in mammalian kidneys carries out excretion?

nephrons

What is the mammalian kidney divided into?

renal cortex (outer) and the renal medulla (inner)

renal artery

carries blood into the kidney

renal vein

carries filtered blood from the kidney

where is urine processed

collecting ducts

After being processed in the collecting ducts, where does urine drain into?

the renal pelvis, ureter, urinary bladder, and the uretha 

where does glomerular filtration happen?

occurs in Bowman’s capsule

What does Bowman’s capsule cup around, what does it do?

glomerulus, does the bulk of filtration of blood from the body 

glomerulus

a ball of arterial capillaries

What tubule descends through the renal medulla and creates the loop of Henle

proximal convoluted tubule

loop of Henle

a U-shaped loop created by the descent of the proximal convoluted tubule through the renal medulla

distal convoluted tubule

formed by the ascent of the tubule

what does the proximal convoluted tubule do?

active reabsorption of of ions, nutrients, and water 

what does the distal convoluted tubule do?

active secretion of H+ and K, passive reabsorption of water, Na, Cl, and HCO₃^- 

what does the descending limb of the Loop of Henle do?

water reabsorption

what does the ascending limb of the Loop of Henle do?

Na and Cl active reabsorption

peritubular capillaries

reabsorb important molecules and ions from the filtrate 

What 3 features interact to conserve nutrients and water, balance salts, and concentrate wastes for excretion?

• Loop of Henle- descends though the medulla and returns again to the cortex

• differences in permeability along the nephron, established by specific membrane transport proteins in each region 

• a concentration gradient of molecules and ions in the interstitial fluid of the kidney, which raises from the renal cortex to the deepest levels of the renal medulla

What do glomerular capillaries have that make them more permeable to water solutes than other capillaries?

pores

What drives fluid containing solutes through the pores of the capillaries and into Bowman’s capsule ?

blood pressures

afferent arteriole

delivers blood to the glomerulus

efferent arteriole

carries blood away from the glomerulus

Which arteriole has a larger diameter and what does this allow?

afferent; helps maintain a high level of glomerular capillary pressure

What do the Na+ and K+ pumps in the epithelium of the convoluted tubule do?

move Na+ and K+ from the filtrate into the interstitial fluid surrounding the tubule 

What cause Cl- to be reabsorbed

a voltage gradient

What reabsorbs glucose, proteins, amino acids, and other nutrients molecules into the interstitial fluid? What does this make the filtrate?

active transport proteins, makes the filtrate hypoosmotic to the interstitial fluid

How does water move from the convoluted tubule to the interstitial fluid?

osmosis (diffusion), aided by aquaporins

After reabsorbing water and nutrients from the convoluted tubule into the interstitial fluid, where does it go?

peritubular capillaries

How do H+ enter the tubule during reabsorption?

active transport

How do the detoxified poisons from the liver enter the tubule during reabsorption?

passive diffusion

Where does the filtrate do after leaving reabsorption in the proximal tubule? What happens here?

the descending limb of the loop of Henle where water is reabsorbed

Is the solute concentration of the interstitial fluid in the medulla where the descending limb passes through higher or lower?

higher, meaning the water concentration is lower and it will diffuse out (facilitated with aquaporins)

As the filtrate gradually reaches the bottom of the Loop of Henle, what peak osmolarity does it reach?

1,200 mOsm/L

What does the reabsorption of salt ions in the medulla help to establish?

the concentration gradient of the medulla 

Where is the solute concentration higher?

near the renal pelvis 

Where is the solute concentration lower?

near the renal cortex 

What does the osmolarity lower to as filtrate gets top the top of the ascending limb?

about 150 mOsm/L

Where is additional water recovered and how? What is it in response to?

in the distal convoluted tubule by osmosis, in response to hormones triggered by changes in the body’s salt concentrations 

What is the osmolarity of urine once it reaches the collecting ducts in comparison to blood?

urine is isosmotic to blood (300 mOsm/L), but still very different in composition

What are collecting ducts are and aren’t permeable to?

• permeable to water

• no permeable to salt ions

As the collecting ducts descend from the renal cortex and into the medulla, what concentration does it encounter? What affect does this have on urine?

a higher solute concentration, which causes water to move out of the urine osmotically, causing the urine’s solute concentration to rise 

Why aren’t the medulla cells damaged by osmotic water ions because of the hyperosmotic state of the interstitial fluid of the medulla?

they are protected by high concentrations of otherwise inert organic molecules called osmolytes in the cytoplasm of medulla cells

How do osmolytes work?

(primarily a sugar alcohol named sorbitol) raises the osmolarity of the cells to match that of the medulla interstitial fluid that surround them

Which adaptations helps to conserve water?

• water conserving activities of the kidneys

• the location of the lungs deep within the body to reduce water loss by evaporation during breathing

• a body covering of keratinized skin that eliminates almost all water loss by evaporation

What does the autoregulation system in the kidney do?

keeps glomerular filtration constant during small variations in blood pressure

What are the two types of autoregulation?

vascular control and feedback control

In vascular control, what happens if there is a rise in blood pressure?

the afferent arteriole is constricted, and the efferent arteriole is dilated, pushing more blood through the glomerulus 

In vascular control, what happens if there is a drop in blood pressure?

the afferent arteriole dilates, and the efferent arteriole constricts, decreasing the blood flow of blood through the glomerulus

juxtaglomerular apparatus

contains specialized tubules that monitor the salt levels of the fluid in the distal tubule during feedback control 

In feedback control, what happens if the salt levels rise in the distal tubule?

chemical messengers (paracrine regulation) act on the adjacent afferent arteriole, causing it to constrict

renin-angiotensin-aldosterone system (RAAS)

• used when excessive Na+ are excreted, blood pressure and volume decrease, and glomerular filtration rate fall below levels that the juxtaglomerular apparatus regulations can restore it 

• cells in the juxtaglomerular apparatus secrete renin into the bloodstream 

• renin cleaves the plasma protein angiotensinogen and turns it into angiotensin I

• angiotensin-converting enzyme (ACE) converts angiotensin II → angiotensin II 

What are the three effects of angiotensin II?

• 1) raised BP by constricting the arterioles 

• 2) stimulates the synthesis and secretion of the steroid hormone aldosterone from the adrenal cortex 

• 3) stimulates the thrist

What does aldosterone do?

raise Na+ reabsorption in kidneys, which raises the osmolarity of body fluids, moves water from tubules to interstitial fluid, and stimulates the secretion of antidiuretic hormone ADH

antidiuretic hormone (ADH)

• increases water reabsorption in into the blood which increases blood volume and pressure

how is osmolarity ? 

via osmoregulatory in the hypothalamus 

How does ADH increase water absorption in the distal convoluted tubule and the collecting ducts ?

promoting the insertion of more aquaporins in the membrane of epithelial cells