A&P II - Urinary System

what does erythropoietin (EPO) do?

increase RBC production

functions of the urinary system

1. regulate blood volume and pressure

• by adjusting volume of water lost in urine and by releasing EPO and renin

2. regulate plasma ion concentrations

• sodium, potassium, chloride, and calcium ions

3. helps to stabilize blood pH

4. conserve valuble nutrients

5. assist liver to detoxify poisons

kidney coverings

renal capsule: collagen fibers cover outer surface

adipose capsule: thick layer that surrounds renal capsule

renal fascia: fibrous layer that anchors kidney to surrounding structures

hilum

point of entry for renal artery and nerves

point of exit for renal vein and ureter

renal sinus

internal cavity within the kidney

renal cortex

superficial portion of the kidney in contact with the renal capsule

renal columns

bands of tissue separating renal pyramids

renal papilla

ducts discharge urine into minor calyx

nephrons

structural and functional units of the kidney

responsible for forming urine

processes of urine formation

1. filtration: renal corpuscle filters the blood to form filtrate (in glomerulus)

2. reabsorption: water and nutrients are put back into the blood from the tubules

   1. secretion: waste products get removed from the blood and into the tubules

filtration

hydrostatic pressure forces water through membrane pores

reabsorption and secretion

diffusion, osmosis, channel-mediated diffusion, carrier-mediated transport

main structures of the nephron

renal corpuscle and renal tubule

glomerulus

specialized capillary bed

large affferent arteriole and narrow efferent arteriole maintain high pressure

juxtaglomerular apparatus (JGA)

monitors blood

secretes EPO and renin

formed by: macula densa and juxtaglomerular cells

functions of the renal tubule

reabsorb useful organic nutrients

reabsorb more than 90% of water in filtrate

secrete waste products that failed to enter renal corpuscle through filtration

cortical nephrons

85% of all nephrons

located within superficial cortex of kidney

juxtamedullary nephrons

15% of nephrons

nephron loops extend deep into medulla

peritubular capillaries connect to vasa recta (long straight capillaries running parallel to the loop of henle)

visceral epithelium

consists of large cells (podocytes) with “feet” (pedicels) that wrap around glomerular capillaries

filtration slits

narrow gaps between adjacent pedicels

materials passing out of blood must be small enough to pass through

blood flow control

mesangial cells: special supporting cells

• control diameter and rate of capillary blood flow

filtration membrane consists of

fenestrated endothelium

lamina densa/basement membrane/basil lamina

is filtration at the renal corpuscle active or passive?

passive process driven by blood pressure

• HP forces water and small solutes across the filtration membrane

glomerular capillaries

fenestrated capillaries with pores that prevent passage of blood cells

• allow diffusion of solutes (plasma proteins)

lamina densa/basement membrane/basil lamina

allows diffusion of only small plasma proteins, nutrients, and ions

filtration slits

finest filters that prevent passage of most small plasma proteins

picky, pickier, pickiest

fenestrae, basement membrane, podocytes

osmolarity

total number of solute particles per liter

directly related to colloid osmotic pressure (ability to draw water towards it)

glomerular filtration is governed by the balance between ____

hydrostatic pressure and colloid osmotic pressure

glomerular hydrostatic pressure (GHP)

pushes water and solute out of plasma into the filtrate

*this pressure should always be largest because the efferent arteriole is smaller than the afferent arteriole

blood colloid osmotic pressure (BCOP)

draws water out of the filtrate and into the plasma (opposing filtration)

capsular hydrostatic pressure (CsHP)

opposes GHP

pushes water and solutes out of the filtrate and into the plasma

glomerular filtration rate (GFR)

the amount of filtrate that the kidneys produce each minute

what does glomerular filtration rate depend on?

filtration pressure

3 levels of GFR control

autoregulation (local level)

hormonal regulation (initiated by kidneys)

autonomic regulation (sympathetic division of ANS)

autoregulation

maintains GFR despite changes in local blood pressure and flow

by constricting/dilating glomerular capillaries, afferent and efferent arterioles

reduced blood flow triggers what?

dilation of afferent arteriole

dilation of glomerular capillaries

constriction of efferent arterioles

rise in renal blood pressure ____?

causes smooth muscle cells to contract

constricts afferent afferent arterioles

decreases glomerular blood flow

hormones regulating GFR

hormones of the RAAS system (increase BP/BV)

ANP and BNP (decrease BP/BV)

sympathetic activation (autonomic regulation)

constricts afferent arterioles

decreases GFR

slows filtrate production

where does reabsorption occur?

at the proximal convoluted tubule (PCT)

tubular cells

absorb organic nutrients, ions, water, and plasma proteins from tubular fluid

release them into peritubular fluid and into peritubular capillary

thick descending limb

fluid flows toward renal pelvis

pumps sodium and cloride ions out of tubular fluid

thick ascending limb

fluid flows toward renal cortex

create high solute concentrations in peritubular fluid

impermeable to water

thin segments on the loop of henle

freely permeable to water but not to solutes

processes of the DCT

active secretion of ions, acids, drugs, and toxins

selective reabsorption of sodium and calcium ions from tubular fluid

• aldosterone stimulates reabsorption of sodium back into the blood

• PTH/calcittriol- absorption of calcium back into the blood

selective reabsorption of water

• ADH brings water back into the blood

well hydrated

little ADH released- large volume of dilute urine

dehydrated

small volume of concentrated urine

what is the goal of urine production?

maintain homeostasis by regulating volume and composition of blood

3 main organic waste products

urea- breakdown of amino acids

creatine- breakdown of creatine phosphate (from cellular respiration)

uric acid- waste product during recycling of RNA

types of carrier-mediated transport

facilitated diffusion (no ATP)

• follows gradient - glucose and amino acids

active transport (ATP)

• can work against gradient

cotransport (2 lane one way street)

countertransport (2 lane highway)