Histo Mod 11 urinary

kidneys

ureter

bladder

urethra

the urinary system

kidney

Paired, bean-shaped

• 12-cm long, 6-cm wide, and 2.5-cm thick

renal cortex

renal medulla

what compose the parenchyma of the kidney

nephron

functional unit of the kidney

renal corpuscle

renal tubules

collecting tubule

major division of the nephron

proximal convoluted tubule

loop of henle

distal convoluted tubule

renal tubules

cortical nephron

juxtamedullary nephron

types of nephron

larger collecting ducts

connecting tubules merge to form

renal papilla

collecting ducts converge in the

minor calyx

from the renal papilla, it delivers urine to the

cortical nephron

Located almost completely in the cortex

• Make up approximately 85% of nephrons

• For removal of waste products and reabsorption of nutrients

juxtamedullary nephrons

About one-seventh of the total

• Lie close to the medulla and have long loops of Henle

• For concentration of the urine

filtration

tubular reabsorption

tubular secretion

renal function

glomerulus

the renal corpuscle is composed of small mass of capillaries called

Glomerular (Bowman's) capsule

the glomerulus is housed within

finely fenestrated

the glomerular capillaries are

Glomerular (Bowman's) capsule

double-walled cup surrounding glomerulus

inner visceral layer of glomerulus

envelopes the glomerular capillaries

outer parietal layer of glomerulus

forms the surface of the capsule

capsular (urinary ) space

between the two capsular layers, receives the fluid filtered through the capillary wall and the visceral layer

outer parietal layer

forms the surface of the capsule

podocytes

filtration slit pores

slit diaphragms

components of the visceral layer

podocytes

together with the capillary endothelial cells compose the apparatus for renal filtration

• unusual stellate epithelial cells

slit diaphragms

Span the adjacent pedicels, bridging the slit pores

• zipper-like, modified and specialized occluding or tight junctions composed of nephrins, other proteins, glycoproteins, and proteoglycans important for renal function.

filtration slit pores

Elongated spaces between the interdigitating pedicels

• 25- to 30-nm wide Slit diaphrag

glomerular basement membrane

Between the highly fenestrated endothelial cells of the capillaries and the covering the podocytes

• 300-360 nm thick

• most substantial part of the filtration barrier that separates the blood from the capsular space

• forms by fusion of the capillary-and podocyte-produced basal laminae

glomerular basement membrane

Laminin and fibronectin bind integrins of both the podocyte and endothelial cell membranes

• the meshwork of cross-linked type IV collagen and large proteoglycans restricts passage of proteins larger than about 70 kDa.

• Polyanionic GAGs are abundant and their negative charges tend to restrict filtration of organic anions

Glomerular Filtration Rate (GFR)

regulated continuously by neural and hormonal inputs affecting the degree of constriction in two arterioles.

• The average GFR = 125 mL/min or 180 L/d

• the kidneys typically filter the entire blood volume 60 times every day

125 mL/min or 180 L/day

average GFR

mesangial cells

resemble vascular pericytes in having contractile properties and producing components of an external lamina

• comprise the mesangium - fills interstices between capillaries that lack podocytes

proximal convoluted tubule

simple cuboidal epithelium

• fill most of the cortex

• PCT cells are specialized for both reabsorption and secretion

proximal convoluted tubule

simple cuboidal epithelium

• have central nuclei and very acidophilic cytoplasm

• cell apex has very many long microvilli that form a prominent brush border in the lumen - facilitates reabsorption

• Peritubular capillaries are abundant in the sparse surrounding connective tissue interstitium, which fills only about 10% of the cortex

loop of henle

a U-shaped structure with a thin descending limb and a thin ascending limb

• diameter: 30 μm • The wall of the thin segments consists only of squamous cells with few organelles (indicating a primarily passive role in transport) • the lumen is prominent

thick ascending limb (TAL)

The thin ascending limb of the loop becomes the _____, with simple cuboidal epithelium and many mitochondria

ascending LOH

Thin limbs: passively reabsorb sodium chloride (NaCl) but are impermeable to water

• TAL: actively transport sodium and chloride ions out of the tubule making that compartment hyperosmotic

descending LOH

This causes water to be withdrawn passively from the thin descending part of the loop, thus concentrating the filtrate

countercurrent multiplier system

The _______ established by the nephron loop and vasa recta is an important aspect of renal physiology in humans

distal convoluted tubule

The ascending limb of the nephron is straight as it enters the cortex and forms the macula densa, and then becomes tortuous as the ____

distal convoluted tubule

Much less tubular reabsorption

• Smaller and flatter simple cuboidal cells than those of the PCT (showing more nuclei)

• Cells have no brush border acidophilic

ty lumens

• Cells have fewer mitochondria, less acidophilus

aldosterone

regulates the rate of Na+ absorption

juxtaglomerular apparatus

monitors the changes in blood pressure and plasma sodium content

utilizes feedback mechanisms to regulate glomerular blood flow and keep the rate of glomerular filtration relatively constant

macula densa

juxtaglomerular granular (JG) cells

lacis cells (mesangial cells)

compositions of the juxtaglomerular apparatus

macula densa

Formed from the contact of the straight part of the distal tubule and the arterioles at the vascular pole of the renal corpuscle of its parent nephron

• Cells here become columnar and closely packed

• apical nuclei, basal Golgi complexes, and a more elaborate and varied system of ion channels and transporters.

macula densa

Monitor the concentration of Na+ and Cl- the TAL

juxtaglomerular granular (JG) cells

A modification of the tunic media of the afferent arteriole

• Smooth muscle cells with a secretory phenotype including more rounded nuclei, rough ER, Golgi complexes, and granules with the protease renin

lacis cells

extraglomerular mesangial cells that have many of the same supportive, contractile, and defensive functions as these cells inside the glomerulus.

papillary ducts (duct of Bellini

Medullary ducts merge to form ____, which deliver urine directly into the minor calyx.

collecting duct

The medullary collecting ducts are the final site of water reabsorption from the filtrate

antidiuretic hormone

The hormone that makes collecting ducts more permeable to water and increases the rate at which water molecules are pulled osmotically from the filtrate.

principal cells and intercalated cells

Two kinds of cells in the DCT and collecting duct

principal cells

Make up the collecting tubules and ducts

• pale-staining with few organelles, sparse microvilli, and unusually distinct cell boundaries • have basal membrane infoldings, consistent with their role in ion transport

• They have a primary cilium among the microvilli

• rich in aquaporins

intercalated cells

help maintain acid-base balance by secreting either H+ or HCO3

tubular (LOH) concentration

collecting duct concentration

urine concentration

tubular (LOH) concentration

the filtrate is exposed to the high osmotic gradient of the renal medulla.

• Water is removed by osmosis in the descending loop of Henle

• sodium and chloride are reabsorbed in the ascending loop.

• This selective reabsorption process is called the countercurrent mechanism and serves to maintain the osmotic gradient of the medulla

countercurrent mechanism

This selective reabsorption process is called the ____ and serves to maintain the osmotic gradient of the medulla

collecting duct concentration

The final concentration of the filtrate through the reabsorption of water begins in the late distal convoluted tubule and continues in the collecting duct.

• Reabsorption depends on the osmotic gradient in the medulla and the hormone vasopressin (antidiuretic hormone [ADH]).

producing hypotonic urine

producing hypertonic urine

control of water loss

producing hypotonic urine

-NaCl reabsorbed by cortical CD

-water remains in urine

producing hypertonic urine

dehydration ⬆️ antidiretic hormone⬆️aquaporin membrane channels⬆️CDs water permeability

more water is reabsorbed

urine is more concentrated

mucosa of urethra, bladder, ureter

lined by the uniquely stratified urothelium or transitional epithelium

umbrella

Most of the apical surface consists of asymmetric unit membranes composed of uroplakins

o assemble into paracrystalline arrays of stiffened plaques 16 nm in diameter

o together with the tight junctions, allow this epithelium to serve as an osmotic barrier

urothelium

is surrounded by a folded lamina propria and submucosa, followed by a dense sheath of interwoven smooth muscle layers and adventitia.

muscularis of urether

thick, moves urine toward the bladder by peristaltic contractions and produces prominent mucosal folds when the lumen is empty

bladder

can hold 400-600 mL of urine, with the urge to empty appearing at about 150-200 mL

lamina propria

submucosa

muscularis

ureter

muscularis of bladder

consists of three poorly delineated layers, collectively called the detrusor muscle (contract to empty the bladder)

urethra

tube that carries the urine from the bladder to the exterior • urethral mucosa has prominent longitudinal folds, giving it a distinctive appearance in cross section

prostatic urethra

membranous urethra

spongy urethra

3 regions of male urethra

prostatic urethra

3-4 cm long, extends through the prostate gland

membranous urethra

a short segment, passes through an external sphincter of striated muscle

spongy urethra

about 15 cm in length

• enclosed within erectile tissue of the penis

urethra in women

is exclusively a urinary organ.

• 3- to 5-cm-long tube

• lined initially with transitional epithelium which then transitions to nonkeratinized stratified squamous epithelium continuous with that of the skin at the labia minora.

• The middle part of the urethra in both sexes is surrounded by the external striated muscle sphincter.

external striated sphincter

The middle part of the urethra in both sexes is surrounded by the ____

renin

an enzyme produced by the juxtaglomerular cells

• reacts with the blood-borne substrate angiotensinogen to produce the inert hormone angiotensin I.

• a protease important for regulation of blood pressure

aldosterone

Regulates the rate of Na+ absorption

• Produced by the adrenal glands

• production of aldosterone is controlled by the body's sodium concen

antidiuretic hormone (ADH)

Vasopressin

• released from the posterior pituitary gland

• renders the walls of the distal convoluted tubule and collecting duct permeable or impermeable to water

antidiuretic hormone (ADH)

as the body becomes dehydrated, makes collecting ducts more permeable to water and increases the rate at which water molecules are pulled osmotically from the filtrate

• Production of ADH is determined by the state of body hydration

renin-angiotensin-aldosterone system

regulates the flow of blood to and within the glomerulus.

• responds to changes in blood pressure and plasma sodium content that are monitored by the juxtaglomerular apparatus

calcitriol

1,25-dihydroxyvitamin D3

• Active form of the steroid prohormone vitamin D, initially produced in the skin and converted in the kidneys

Erythropoietin

a glycoprotein growth factor that stimulates erythrocyte production in red marrow when the blood O2 level is low