Anatomy 2

List the kidney functions

Filters blood plasma - separates and eliminates waste, returns useful chemicals to blood

Regulates blood volume and pressure - eliminates or conserves water as needed

Regulates osmolarity of body fluids - controls amount of water and solutes eliminated

Secretes the enzyme renin - activates hormonal mechanisms that control BP and electrolyte balance

Secretes erythropoietin - controls RBC count

Regulates PCO2 and acid-base balance

Detoxifies - eliminates free radicals, toxins and drugs

Promotes gluconeogenesis - from amino acids during extreme starvation

Completes final step in synthesizing hormone calcitrol - contributes to calcium homeostasis

Define “waste” and “metabolic waste” and list some examples

Waste - any substance that is useless to the body (toxins, drugs, hormones, salts, hydrogen ions, excess water)

Metabolic waste - produced by the body (CO2 mostly expended by lungs but some in urine, and nitrogenous wastes)

Describe the cellular processes for producing nitrogenous wastes

• Urea (50% of nitrogenous wastes), protein catabolism. Proteins → amino acids → NH2 removed → forms ammonia → liver converts to urea

• Uric acid, nucleic acid catabolism

• Creatinine, creatine phosphate catabolism

Nitrogenous Wastes in Blood

Blood urea nitrogen (normal: 10-20mg/dL)

Define azotemia and uremia

Azotemia - build up of nitrogenous wastes in the blood

Uremia - toxic effects as wastes accumulate (diarrhea, vomiting, dyspnea, cardiac arrhythmia, convulsions, coma, death). If kidneys fail, dialysis must be started to artificially remove wastes from blood

List the systems of the body that excrete wastes and the types of wastes excreted by

each

Respiratory system: CO2

Integumentary system: water, salts, lactic acid, urea

Digestive system: water, salts, CO2, lipids, bile pigments, cholesterol

Urinary system: many metabolic wastes, toxins, drugs, hormones, salts, H+, and water

Describe and illustrate the anatomy of a kidney

Shaped like a kidney bean (hilum - point of entry/exit for nerves, blood vessels, ureter, etc)

Adrenal glands located on superior surface

T12-L3 (right kidney slightly lower due to liver)

About the size of a bar of soap

List the three layers of connective tissues that are associated with the kidney

Renal fascia: outer layer, binds kidney ureter and bladder to abdominal wall

Perirenal fat capsule: fatty middle layer, cushions kidney

Fibrous capsule: inner sac, encloses kidney like cellophane wrap

Describe the renal parenchyma and all the structures of the internal kidney

Parenchyma - glandular tissue that forms urine (cortex and medulla)

Kidney sinus - contains blood and lymphatic vessels, nerves, urine collecting ducts and fat

Trace the pathway of blood through the kidney

Circulation

Renal arteries → segmental arteries → interlobar arteries (up renal columns) → arcuate arteries (over pyramids) → cortical radiate arteries (up into cortex) → branch into afferent arterioles (each supplying one nephron) → leads to glomerulus (ball of capillaries)

Drainage

Glomerulus → efferent arterioles → peritubular capillaries OR vasa recta, cortical radiate veins, arcuate veins, interlobar veins → renal vein → inferior vena cava

Describe the structure of a nephron and its function

Functional units of kidney (1.2 million nephrons per kidney at birth)

Renal corpuscle: filters blood plasma

Renal tubule: converts filtrate into urine

Describe and illustrate the renal corpuscle and renal tubule

Renal Corpuscle:

• Parietal layer (outer layer - simple squamous epithelium)

• Visceral layer (inner layer of podocytes, wrap around capillaries of glomerulus)

• Capsular space (separates the 2 layers)

Renal Tubule:

• Proximal convoluted tubule

• Nephron loop (hoop of henle)

• Distal convoluted tubule

• Collecting duct

Characterize the collecting and papillary ducts

Collecting duct

– receives fluid from the DCTs of several nephrons as it passes back into the medulla

Papillary duct

– merger of several collecting ducts

– 30 papillary ducts end in the tip of each papilla

– Collecting and papillary ducts lined with simple cuboidal epithelium

Compare two types of nephrons

Cortical nephrons (85%): short loops, branch off into peritubular capillaries

Juxtamedullary nephrons (15%): long loops, maintains medullary salt gradient for water conservation, branch off into vasa recta

List the structures and type of fluid that flows through the kidney

Glomerular filtrate: glomerular capsule

Tubular filtrate: PCT, DCT, nephron loop

Urine: collecting duct, papillary duct, minor calyx, major calyx, renal pelvis, ureter, urinary bladder, urethra

List and describe the 4 processes involved in urine production

Blood plasma → urine

1. Glomerular filtration: plasma-like filtrate

2. Tubular reabsorption: returns solutes to bloodstream

3. Tubular secretion: removes additional wastes from blood

4. Water conservation: returns water to bloodstream

How much of the glomerular filtrate is reabsorbed into the bloodstream?

99%

Explain the mechanism of glomerular filtration and describe the filtration membrane

Water and some solutes in the blood pass from capillaries of the glomerulus into the capsular space of the nephron

FILTRATION MEMBRANE:

Fenestrated endothelium - 70-90nm pores, small enough to exclude blood cells

Basement membrane - proteoglycan gel, excludes molecules > 8nm, a few large particles may penetrate, but most are held back, negatively charged, blood plasma 7% protein, glomerular filtrate 0.03%

Filtration slits - podocyte arms have pedicels with negatively charged filtration slits to exclude large anions

List the substances that can/cannot cross the filtration membrane

Can: water, electrolytes, glucose, fatty acids, amino acids, nitrogenous wastes, vitamins

Can’t: calcium, iron, thyroid hormone

Define proteinuria, albuminuria and hematuria

Proteinuria: protein in urine

Hematuria: blood in urine
Albuminuria:

Explain the situations in which protein may be found in the urine

• Prolonged, strenuous exercise - greatly reduces perfusion of kidney, glomerulus deteriorates

Explain the relationship of blood hydrostatic pressure (BHP), capsular pressure (CP) and

colloid osmotic pressure (COP) in the process of glomerular filtration

Blood hydrostatic pressure (BHP):

• Much higher in glomerular capillaries, 60 mm Hg compared to 10-15 in most other capillaries.

• Afferent arteriole is larger than efferent arteriole • larger inlet and smaller outlet

Hydrostatic pressure (CP) in capsular space

• 18 mm Hg due to high filtration rate and continual accumulation of fluid in the capsule

Colloid osmotic pressure (COP) of blood - 32 mm Hg

• filtrate is almost protein-free → no significant COP

Calculate net filtration pressure given normal values

– 60out – 18in – 32in = 10 mm Hgout

Describe the effects of high glomerular blood pressure

Makes kidneys vulnerable to hypotension (rupture of glomerular capillaries, scarring of the kidneys, atherosclerosis of renal blood vessels, renal failure

List average rates of glomerular filtration for males and females

males - 180 L/day

females - 150 L/day

Explain the effects of high/low GFR

Too high: fluid flows through renal tubules too rapidly for them to reabsorb the usual amount of water and solutes, urine output rises. causes dehydration and electrolyte depletion

Too low: too many wastes reabsorbed, azotemia may occur

Explain the relationship between GFR and blood pressure

GFR is controlled by adjusting glomerular blood pressure from moment to moment

List three mechanisms to regulate GFR and describe how each mechanism works

Renal autoregulation: the ability of the nephrons to adjust their own blood flow and GFR without nervous or hormonal control. Allows them to maintain stable GFR despite changes in arterial blood pressure. 2 methods - myogenic mechanism & tubuloglomerular feedback

Sympathetic nervous system control:

Hormonal control:

Contrast the myogenic mechanism and tubuloglomerular feedback

myogenic mechanism: based on smooth muscle contracting when stretched. Increased arterial blood pressure stretches afferent arteriole, arteriole constricts and prevents blood flow into the glomerulus from changing much. when blood pressure falls, afferent arteriole relaxes, allows blood flow into glomerullus.

tubuloglomerular feedback: glomerulus receives feedback on the status of tubular fluid and adjusts.

Describe the cells of the juxtaglomerular apparatus, and explain how they function

Macula densa (end of nephron loop): senses variations in flow or fluid composition and secretes a paracrine that stimulates JG cells

Juxtaglomerular cells (enlarged smooth muscle in afferent arteriole): dilate or constrict arterioles when stimulated by the macula, secrete renin in response to drop in blood pressure

Mesangial cells: between afferent and efferent arterioles and among capillaries of the glomerulus (connected to macula densa and JG cells by gap junctions, constrict or relax to regulate flow)

Explain how the sympathetic nervous system affects GFR

Sympathetic nerve fibers richly innervate the renal blood vessels

Sympathetic nervous system and adrenal epinephrine constrict the afferent arterioles in strenuous exercise or acute conditions like circulatory shock

– Reduces GFR and urine output

– Redirects blood from the kidneys to the heart, brain, and

skeletal muscles

– GFR may be as low as a few milliliters per minute

List the hormones that regulate GFR, and describe how each functions

Renin - Secreted by kidneys when they sense a drop in blood pressure (first step in pathway to angiotensin II)

Angiotensin II - potent vasoconstrictor raising BP throughout body, constricts efferent arteriole raising GFR despite low BP, lowers BP in peritubular capillaries enhancing reabsorption of NaCl and H2O, stimulates adrenal cortex

Aldosterone - secreted by adrenal cortex, promotes Na+ and H2O reabsorption in DCT and collecting duct, stimulates posterior pituitary

ADH - secreted by posterior pituitary, promotes water reabsorption by collecting duct, stimulates thirst

Explain the processes of tubular reabsorption and secretion

1. Glomerular filtration creates a plasmalike filtrate of the blood

2. Tubular reabsorption removes useful solutes from the filtrate, returns them from the blood

3. Tubular secretion removes additional wastes from the blood, adds them to filtrate

4. Water conservation removes water from the urine and returns it to blood, concentrates wastes

PCT reabsorbs 65% of glomerular filtrate and returns it to peritubular capillaries

– Much reabsorption by osmosis and cotransport mechanisms linked to active transport of sodium

Nephron loop reabsorbs another 25% of filtrate

DCT reabsorbs Na+, Cl−, and water under hormonal control, especially aldosterone and ANP

The tubules also extract drugs, wastes, and some solutes from the blood and secrete them into the tubular fluid

DCT completes the process of determining the chemical composition of urine

Collecting duct conserves water

Describe the structure of the proximal convoluted tubule (PCT)

Tubular reabsorption

– useful substances from tubular fluid back to the blood

– reabsorbs 65% of GF to peritubular capillaries!

Tubular secretion

– wastes from the blood to the tubular fluid

Great length, prominent microvilli and abundant mitochondria for active transport

Reabsorbs greater variety of chemicals than other parts of nephron

Describe two routes of reabsorption

Transcellular route

– Substances pass through the cytoplasm of the PCT epithelial cells

Paracellular route

– Substances pass between PCT cells

– Junctions between epithelial cells are quite leaky and allow significant amounts of water to pass through

– Solvent drag—water carries with it a variety of dissolved solutes

Taken up by peritubular capillaries

Explain why there is a solute transport maximum

There is a limit to the amount of solute the renal tubules can reabsorb, limited by the number of transport proteins, transport maximum is reached when transporters are saturated

Explain the purpose of tubular secretion

Extracts additional chemicals/wastes from capillary blood and secretes them into tubular fluid

Waste removal

• Urea, uric acid, bile acids, ammonia, catecholamines, prostaglandins, and a little creatinine (secretion of uric acid compensates for its reabsorption earlier in PCT)

• Clears blood of pollutants, morphine, penicillin, aspirin and other drugs (why we need to take prescriptions multiple times/day to keep pace with the rate of clearance)

Acid-base balance

• Secretion of hydrogen and bicarbonate ions help regulate pH of body fluid

Describe the structure of the nephron loop

Primary function of nephron loop is to generate a salinity gradient in the renal medulla that enables collecting duct to concentrate the urine and conserve water

List the substances that move out of the nephron loop in the thick and thin segments

Only the thin segment is permeable to water

Electrolyte reabsorption from filtrate:

Thick segment reabsorbs 25% of Na+, K+, and Cl− (Ions leave cells by active transport and diffusion)

• NaCl remains in the tissue fluid of renal medulla

• Water cannot follow since thick segment is impermeable

Tubular fluid very dilute as it enters distal convoluted tubule

Describe the composition of tubular fluid in the distal convoluted tubule

Fluid arriving in the DCT still contains about 20% of the water and 7% of the salts from glomerular filtrate

List and describe the mechanisms of action of the hormones that act upon the DCT and

collecting duct

DCT and collecting duct reabsorb variable amounts of water salt and are regulated by several hormones

– Aldosterone

– Atrial Natriuretic Peptide

– ADH

– Parathyroid hormone

Describe the structure and function of the collecting duct

Collecting duct (CD) begins in the cortex where it receives tubular fluid from several nephrons

As CD passes through the medulla, it reabsorbs water & concentrates urine up to 4X

Medullary portion of CD is more permeable to water than to NaCl

As urine passes through the increasingly salty medulla, water leaves by osmosis, concentrating urine

Define water diuresis

drinking large volumes of water will produce a large volume of hypotonic urine

– Cortical portion of CD reabsorbs NaCl, but it is impermeable to water

– Urine concentration may be as low as 50 mOsm/L

Explain when and how the body produces hypotonic and hypertonic urine

Hypertonic:

Dehydration causes the urine to become scanty

and more concentrated

– High blood osmolarity stimulates release of ADH

and then an increase in synthesis of aquaporin

channels by renal tubule cells

– More water is reabsorbed by collecting duct

– Urine is more concentrated

• If BP is low, GFR will be low

– Filtrate moves more slowly and more time for

reabsorption

– More salt removed, more water reabsorbed, and

less urine produced

Explain the purpose of the countercurrent multiplier

Describe how the nephron loop acts as a countercurrent multiplier

Explain the function of the countercurrent multiplier

Contrast countercurrent multiplier and countercurrent exchange

Explain the function of the countercurrent multiplier

Describe the composition and properties of urine with respect to appearance, odor, specific gravity, osmolarity, pH and chemical composition

Contrast normal urine volume, polyuria, oliguria and anuria

Explain the mechanisms by which diuretics affect urine volume

Describe the structure and function of the ureters and urinary bladder

Compare the male and female urethra

Explain the mechanisms for micturition in infants and adults

Describe the composition, causes and effects kidney stones and how they are treated

Explain why UTIs are more common in females than males

Define cystitis, pyelitis and pyelonephritis

Describe acute glomerularnephritis, hydronephrosis, nephroptosis and nephrotic

syndrome

Contrast acute and chronic renal failure

Describe urinary incontinence

List the different types of diabetes and their causes