a + p II midterm 3

Overview of kidney functions

maintain the constancy of the body’s internal environment (homeostasis) by regulating the volume and composition of the ECF (interstitial fluid)

How are kidney functions accomplished?

kidneys balance the intake, production, excretion, and consumption of many organic and inorganic compounds

Balancing the intake requires the kidneys do what tasks?

1. regulation of blood ionic composition + pH

2. excretion of organic waste products

3. blood pressure regulation

4. hormone production

5. maintain blood osmolarity

6. regulation of blood pH

How does regulation of blood ionic composition and pH occur?

renal excretion of Na+, K+, Ca++, Mg++, H+, and HCO3- balances the intake and excretion of these substances through other routes

• ex. GI tract and skin

What are examples of those excreted organic waste products?

urea, creatinine, uric acid

• increased levels → kidney failure

2 ways of blood pressure regulation in kidney

1. by way of renin formation and release (renin is then involved in activating the angiotensin-aldosterone)

2. by way of renal control of blood volume

hormone production in kidney

1. through the formation and release of hormones

   1. erythropoietin which stimulates RBC production

   2. Calcitriol the active form of Vit D

How does kidney maintain blood osmolarity

separately regulates loss of H2o and loss of solute

how does regulation of blood pH occur in the kidney

involves H+ and HCO3- balance

what is kidney failure

substances accumulating in the blood and extracellular fluid → changes in the bodies internal environment → decrease in body cell function → death

Anatomy and Histology of the Kidneys

• paired, reddish-brown organs

• on upper posterior wall of the abdominal cavity, between the muscles of the back (t12-l3) and peritoneal cavity (retroperitoneal)

• capped by adrenal (suprarenal) gland

• right kidney lower than left because of liver

Why does kidney location benefit surgery access?

it can be approached surgically through the posterior body wall without opening the peritoneal cavity

external anatomy of the kidneys

• bean shaped

• convex lateral border, concave medial border

• hilum

what is the hilum in the kidneys

indentation which most structures enter (renal artery) or leave (renal vein, ureter) the kidney

renal sinus

internal space the hilum opens into which contains the renal vessels and the renal pelvis and calyces

tissue layers surrounding the kidneys

renal capsule, adipose capsule, renal fascia

renal capsule

innermost layer, directly covers the kidney; fibrous

adipose capsule

mass of perirenal fat surrounding the renal capsule

renal fascia

surrounds the adipose capsule, completely enclosing and anchoring the kidney to the posterior abdominal wall

Internal anatomy of the kidneys

divisions and collecting system

divisions

the renal parenchyma is divisible into 2 regions

1. renal cortex

2. renal medulla

renal cortex

lighter outer layer (deep to renal capsule)

• divided into an outer “cortical zone” and an inner “juxtamedullary zone”

extensions of the cortex (renal columns) extend into the medulla between the pyramids

renal medulla

deep to the cortex

• formed by several triangular renal pyramids

• orientation of pyramids: broad bases covered by cortex and their tips

  • papillae

papillae

project toward the renal pelvis

• renal pyramids separated by columns

• blood vessels the supply cortex and medulla flow through columns

• renal lobe

renal lobe

one pyramid + overlying cortex + ½ adjacent column

collecting system divided into?

minor calyces, major calyces, renal pelvis

minor calyces

each minor calyx is funnel-shaped with a papilla projecting into it = 8-18/kidney

major calyces

each major calyx is formed by the fusion of several minor calyces = 3/kidney

renal pelvis

formed by the fusion of the major calyces + the expanded upper part of the ureter

what are nephrons?

the functional units of the kidneys where urine is formed

• 1 million/kidney

Types of nephrons

cortical, juxtamedullary

cortical nephron characteristics

80-85% of the nephrons in the kidney

• short loops of Henle, which only descend only as far as the outer medulla

juxtamedullary nephron characteristics

corpuscles located at the junction of the cortex and medulla of the kidney

• long loops of Henle which penetrate deep into the medulla and sometimes read the tip of the renal papillae

What are juxtamedullary nephrons important in?

the counter-current system by which the kidneys concentrate urine

Each nephron consists of what 2 parts

the glomerulus, renal tubule

what is the glomerulus

a network of parallel capillaries (20-40 capillary loops)

• protrudes into the Bowman’s capsule

• located in kidneys cortex

what is the renal tubule

epithelial line tube with various regions that differ from one another anatomically (epithelial variations)

• bowmans capsule, proximal convoluted tubule, loop of henle, distal convoluted tubule, “collecting tubule” renal corpuscle

what is the glomerula capsule

a double walled cup formed by the proximal end of the renal tubule

what is glomerular filtration

a process occurring in the corpuscles important in urine production

• some of the blood plasma (except for protein) passes out of the glomerular capillaries and exits the space (capsular space) between the inner and outer layers of the capsule

glomerular filtrate

fluid formed by this process

glomerular capsule: parietal layer of capsule made up of?

simple squamous epithelials

glomerular capsule: visceral layer of capsule made up of?

composed of specialized cells called podocytes

• form 3 processes = foot processes = pedicels

what do podocytes adhere to?

basal lamina covering the capillary endothelium

slit pores

the foot processes of one podocyte interdigitate with those of adjacent podocytes → network of small clefts between them = filtration slits

a thin slit membrane extends between what? Restricting what?

foot processes barrier, restricting the passage of some molecules through slits

glomerular capillaries

endothelium formed by a single layer of squamous cells

• endothelial cells have small pores

what is the filtration barrier (membrane)

the separation between the blood in the glomerular capillaries from the capsular space

consisting of:

1. the fenestrate endothelium

2. basal lamina (basement membrane)

3. slit membranes that cover the filtration slits

many substances are able to pass through this barrier = those substances less than 3 nm diameter

most substances present in the plasma except most plasma proteins is?

glomerular filtrate

what are negatively charged glycoproteins associated with?

the filtration barrier and influence the movement of molecules across the barrier

speed molecules of the same size

positively charged molecules > neutral molecules > negatively charged molecules

damage to the filtration membrane causes

albuminuria (proteinuria) or hematuria (blood)

proximal convoluted tubule

the region of the renal tubule beyond the glomerular capsule whose lumen is continuous with the capsular space

• located in cortex; twisted

renal tubule wall

single layer of columnar cells with microvilli extending into the lumen (brush border)

• increase surface area for reabsorption and secretion

loop of henle descending limb

part of each loop that descends into the medulla; wall = thin squamous epithelium therefore

= thin segment of loop

loop of henle ascending limb

formed in the medulla by hairpin turn the loop takes

• passes out of medulla → cortex

  • wall = cuboidal cells (thick); squamous cells (thin)

distal convoluted tubule

the highly coiled region beyond the distal straight tubule

• wall = single layer of cuboidal cells with few microvilli

collecting tubule

a large tubule in which distal convoluted tubules of several nephrons empty into → passes through a medullary renal pyramid → joining together of adjacent collecting tubules to form larger ducts that open on the papilla → minor calyx

blood vessels of the kidneys: renal arteries

each kidney receives a renal artery = a major branch from descending aorta

How much of the total cardiac output do the kidneys recieve?

20% , 1.1 L/min of blood passing through the two kidneys

• little of this blood is for kidney cell nutrition

what is the purpose of large blood flow

maintenance of the blood homeostasis

interlobar arteries travel between the

pyramids

what are arcuate arteries

arching branches given off by the interlobar arteries at the bases of the pyramids (cortex-medulla junction); run parallel to kidney surface

what are interlobular arteries

small branches given off at intervals by the arcuate arteries and which travel through the cortex toward the kidney surface

what are afferent arterioles

divisions of the interlobular arteries; each supplies a renal corpuscle to form the capillary network (glomerulus - where glomerular filtrate made)

what are efferent arterioles

blood leaves the glomerulus through this arteriole

what are peritubular capillaries

divisions of the efferent arterioles which form networks surrounding the renal tubules

what is the vasa recta

thin walled vessels which extend from the efferent arteriole of the juxtamedullary nephrons to supply the loop of Henle and collecting tubules in the medulla\

• has IMPORTANT role in URINE

what empties into interlobular veins →> renal veins

peritubular capillaries or vasa recta

• veins follow course of arteries with the same names

what is the flow of blood through 2 sequential series of capillary beds?

arteriole → glomerulus → arteriole → peritubular capillaries

what does smooth muscle in arteriole walls permit

• constriction or dilation associated with conditions

• fairly constant blood pressure in the glomerulus can be maintained

• efficient kidney function

difference between glomerular capillaries and peritubular capillaries

gc produce filtrate, pc reabsorbs filtrate

what is the juxtaglomerular complex (apparatus)

a combination of specialized tubular and vascular cells located at the vascular pole where the afferent and efferent arterioles enter and leave the glomerulus

where is the juxtaglomerular complex located

in the cortex and where the tubule contacts the afferent arteriole

what two cells is the juxtaglomerular apparatus made up of

juxtaglomerular cells and macula densa cells

what are juxtaglomerular cells

specialized smooth muscle cells of the afferent arteriole that contain secretory granules (contain renin)

what are macula densa cells

cells of the macula densa = region of the tubule which contacts the juxtaglomerular cells

• cells appear taller (chemo or osmoreceptors)

what are macula densa cells invovled in

blood pressure and Na+ regulation

three basic renal processes

1. glomerular filtration

2. tubular secretion

3. tubular reabsorption

characteristics of glomerular filtration

plasma filtered out of the glomerular capillaries into the glomerular (Bowman’s) capsule

• not very selective, passive

what is glomerular filtrate made up of

water and other plasma compounds that enter the capsule (the filtrate in the renal tubules)

• plasma composition - protein

• passive not selective

characteristics of tubular reabsorption

process which removes H2O ions, glucose, etc. from the tubular fluid and returns it to the blood as it flows through the peritubular caps and vasa recta (can be active or passive)

characteristics of tubular secretion

materials that enters the tubular fluid which didn’t enter the glomerular capsule during glomerular filtration (can be active or passive)

• removes substances from blood

secretion and reabsorption can be under ______ control

hormonal

the fluid remaining in the tubules can eventually be excreted as __________

urine

What percentage of blood plasma entering the kidneys is filtered from the glomerular capillaries to glomerular capsule → glomerular filtrate

16-20

average amount of glomerular filtrate/day produced

180L (45 gal)

• 99% reabsorbed → 1% (1-2L) excreted as urine/day

What is interesting about the filtration barrier between the plasma and capsule space

increased permeability

net filtration pressure: glomerular blood hydrostatic pressure

factor FAVORING filtration OUT of the glomerular capillaries → glomerular capsule

HPg > 55mmHg

net filtration pressure: capsular hydrostatic pressure

factors opposing filtration out of the glomerular capillaries into the glomerular capsule

• pressure of lfuid in Bowman’s capsule

• CHP, HPc

• 15 mmHg

osmotic force exerted by the unfiltered plasma proteins that remain within the glomerular capillaries (BCOP)(OPg)(OPg = 30 mmHg)

net filtration pressure equation

(HPg) - (OPg + HPc)

55 - (30+15) = 10 mmHg out

• favors movement of materials out of the capillaries INTO capsule space

What do HPg, OPg, or HPc do ?

changes in glomerular filtration rate (GFR) (amount of filtrate/min)

Glomerular filtration rate equation

NFP x Kf

What three mechanisms control GFR

1. renal autoregulation

2. neural regulation

3. hormonal regulation

ex. one would expect changes in arterial blood pressure → comparable changes in HPg BUT this influence is NOT GREAT on the GFR because of the mechanisms

What do kidneys intrinsic autoregulatory mechanisms do?

fairly stable GFR over a wide range of systamic arterial BPs

What does increased arterial blood pressure cause (GFR)

small increase in GFR

What happens if the GFR too fast

increased flow → not enough time to reabsorb all

what happens if the GFR too slow

decreased flow → even waste gets reabsorbed

myogenic mechanism when increased arterial blood pressure

response of arteriole smooth muscle

increased arterial BP → increased afferent arteriole BP → stretching of afferent arteriole wall

what does afferent arteriole constriction cause

limitation of blood flow into the glomerulus → prevents an increased HPg and therefore prevents an increased GFR despite increased arterial BP

myogenic mechanisms when decreased arterial blood pressure

decreased afferent arteriole BP → decreased stretch on afferent arteriole wall (smooth muscle relaxation)