Physiology - URINARY

What do kidneys do?

produce urine

What do ureters do?

transport urine

What does the urinary bladder do?

store urine

What does the urethra do?

excrete urine

What are the homeostatic functions of the urinary system?

• water balance

• electrolyte balance

• removal of waste

• control of blood pressure

• acid balance

Major functions are carried out at the…

nephron

What are nephrons?

functional unit of the kidney

filtration, reabsorption, secretion

Anatomy:

• Glomerular apparatus

  • afferent/efferent arterioles

  • flomerular capillaries

  • bowmans capsule

• proximal convoluted tube

• loop of henle

  • descending limb

  • ascending limb

• distal convoluted tubule

• collecting duct

What are blood vessels in the urinary system?

allow nephron function by maintaining concentration gradients

• efferent arteriole: carries filtrate out glomerulus

• glomeruluar cappilaries

• afferent arteriole: carries blood into flomerulus to be filtered

• peritular capillaries

• vasa recta

What is filtration in the nephron?

bulk flow into nephron (glomerulus)

blood → nephron

What is reabsorption in the nephron?

putting a substance back into blood

tubular system → blood

What is secretion in the nephron?

putting specific substance into nephron (waste)

blood nephron →

What is the glomerular apparatus?

glomerular apparatus filtrates blood by mediating the diffusion of molecules from blood vessels into the bowmans capsule lumen

What is filtrate?

solution comprised of water and filtered molecules

What sets glomerular cappilaries apart from other capillary beds?

Fed by: Afferent arteriole

Drained by Efferent Arterioles

• more control

What do afferent / efferent arterioles do?

regulate glomerular pressure and contribute to a pressure gradient

What is the glomerular filtration barrier? (nephron)

regulates diffusion across capillary walls

• fenestrations: holes in capillary

• podocytes: cells covering vessel

What is proteinuria?

high levels of protein in urine

• result in kidney disease where podocytes have been damaged

What is hematuria?

blood in urine due to glomerular and extraglomerular damage

condition severly manifest based on the concentration of blood in urine

• gross hematuria (high concentration)

• micro hematuria (low concentration)

What is the glomerular filtration rate (GFR)?

rate at which diffusion takes place at the glomerulus, change depends on body needs

What is GFR affected by?

• blood pressure: dependent of blood volume, vasoconstriction, vasodilation, and cardiac output

• colloid osmotic pressure: plasma concentration of filtrate molecules

• capsular hydrostatic pressure: pressure inside bowmans capsule

Net outward pressure: combination of all pressures

Why must GFR be regulated?

• if blood flows too quickly there will not be enough time to filter blood

• if blood flows too slowly, capsular hydrostatic pressure may increase

What happens when afferent arterioles are vasoconstricted?

1. decrease blood flow into the capillaries (slows down)

2. glomerular pressure decreases

3. GFR decreases

What happens when efferent arterioles are vasocontricted?

1. decrease blood flow out of the capillaries

2. glomerular pressure increases

3. GFR increases

What happens to GFR under sympathetic stimulation?

1. both arterioles contrict

2. HOWEVER!! influence is greatest at afferent arteriole (it constricts more)

3. decrease blood flow into the capillries

4. NET EFFECT: blood flow into the capillaries decrease

5. GFR decreases

fight or flight, no prioritize peeing

decrease blood flow into glomerulus

(constriction of afferent arteriole)

What happens to GFR under the parasympathetic nervous system?

increases blood flow into glomerulus

(vasodilation of afferent arteriole)

How is GFR affected by the endocrine syste,?

renin/angiotensin increase pressure in glomerulus

(constriction of efferent arteriole)

renin / angiotensin steps

1. HYPERTENSION (stimulus) triggers release of renin from the KIDNEYS (GRANULAR cells)

2. renin promotes conversion: ANGIOTENSINOGEN → ANGIOTENSIN 1

3. Angiotensin converting enzyme: ANGIOTENSIN 1 → ANGIOTENSIN 2

What are the effects of angiotensin 2?

1. promotes systemic VASOCONTRICTION (increase blood pressure in afferent arterioles)

2. promotes production and release of aldosterone by adrenal gland?

What does aldosterone do?

promotes SODIUM RENTENTION in kidneys

released from adrenal glands in response to low BP

• water follows sodium due to osmosis

• retention of water increases BP

How does angiotensin affect cardiac activity and GFR?

• increases heart rate

• decreases GFR

What is ADH? (antidiuretic hormon / vasopressin)

released from posterior pituitary

release stimulated by high osmotic pressure of blood and aldosterone

increases the number of OPEN AQUAPORINS in DCT and COLLECTING DUCT

HELPS THE BODY RETAIN / REABSORB WATER

happens when body is dehydrated

What is reabsoption?

diffusion of a molecule from:

1. lumen of the nephron

2. into the nephron cells

3. into the tissues / blood vessels surrounding the nephron

affected by concentration gradients across segments

What is the proximal convoluted rubule?

• passive h2o reabsorption

  • aquaporins

  • hypotonic → hypertonic

  • goes down concentration gradient

• active Na + reabsorption

  • need H+ to transport, goes against concentration gradient

  • also facillitates H2O movement

  • active Na+ / H+ antiport moves Na+ inside PCT to PCT cells. H+ out of PCT cells into filtrate

  • Na+ pumped out of cell into blood w/ Na+ / K+ ATPase

• secretion - elimination of urea, excess ions, and prescription drugs

What is renal clearance?

how fast a substance is removed from the plasma by the kidney

• affected by substance concentration and GFR

What is the descending limb? (Loop of Henle)

passive H2O reabsorption due to aquaporins

What is the ascending limb?

thin region: ion reabsoption

Thick region: secondary active absorption

What are cortical nephrons? (2 types of nephrons)

SHORT loops feature low rate of reabsoption

• low interstitial osmolarity

What are juxtamedullary nephrons? (2 types of nephrons)

LONG loops feature high rate of reabsoption

steps that occur in descending limb

1. water moves passively out of the descendin glimb

2. water returns to peritubular capillaries

3. filtrate becomes more hypertonic

4. filtreate at the distal part of the tubule is super concentrated

steps that occur in the ascending limb

1. passive reabsoption at thin segments

2. active reabsorption at thick segments

3. most ions remain at the instertitual fluid

4. filtrate becomes dilute