Urinary system

What does the urinary system do?

removes waste products from the body, especially the blood

Functions of the Kidneys

• Filter blood and excrete toxic metabolic wastes

• Regulate blood volume, pressure, and osmolarity

• Regulate electrolytes and acid-base balance

• Secrete erythropoietin, which stimulates the production of red blood cells

• Help regulate calcium levels by participating in calcitriol synthesis

• Clear hormones from blood

• Detoxify free radicals

• In starvation, they synthesize glucose from amino acids

Waste

any substance that is useless to the body or present in excess of the body’s needs

Metabolic waste

waste substances produced by the body

Urea formation

proteins→ amino acids→ NH2 removed → forms ammonia→ liver converts ammonia to urea

Uric acid

product of nucleic acid catabolism

Creatinine

product of creatine phosphate catabolism

Blood urea nitrogen

level of nitrogenous wastes in blood

What is the biggest component of nitrogen in our blood?

urea

Azotemia

too much nitrogen in blood

what can azotemia indicate?

renal insufficiency

Uremia

disorder associated with the digestive tract, stemming from toxicity from nitrogenous wastes

Excretion

separating wastes from body fluids and eliminating them

What are the four systems that excrete waste products?

Respiratory, integumentary, digestive, and urinary

What does the urinary system excrete?

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

Position of kidney

Retroperitoneal along with ureters, urinary bladder, renal artery and vein, and adrenal glands

About what size are the kidneys?

about the size of a bar of soap

What type of tissue surrounds the kidney?

adipose

Hilum

place on kidney where input and output happens

What does the hilum all receive?

renal nerves, blood vessels, lymphatics, and ureter

What are the three connective tissues coverings of the kidney?

Renal fascia, perineal fat capsule, fibrous capsule

Renal fascia

immediately deep to parietal peritoneum, Binds it to abdominal wall

perineal fat capsule

cushions kidneys and holds it in place

Fibrous capsule

protects it from trauma and separates it from adipose tissue

Renal parenchyma

glandular tissue that forms urine

Renal sinus

cavity that contains blood, lymphatic vessels, nerves and urine collecting structures

What are the two zones of the renal parenchyma?

outer renal cortex and inner renal medulla

Inner renal medulla components

renal columns and pyramids

Renal columns structure

extensions of the cortex that project inwards towards the sinus

Renal pyramids structure

6 to 10 with broad base facing cortex and renal papilla facing sinus

Lobe of kidney

one pyramid and its overlying cortex

Minor calyx

cup that nestles the papilla of each pyramid, collects its urine

Renal pelvis

formed by convergence of 2 or 3 major calyces

Ureter

a tubular continuation of the pelvis that drains urine down to the urinary bladder

Why do kidneys get a disproportionate amount of blood for their size?

they are the organs that are filtering it of toxins and wastes

renal artery

capillary bed where blood is actually filtered

What does the renal artery divide into?

segmental arteries

What do segmental arteries give rise to?

interlobar arteries, arcuate arteries, cortical radiate arteries, afferent arterioles

Interlobar arteries

up renal columns, between pyramids

Arcuate arteries

over pyramids

Cortical radiate arteries

up into cortex

Afferent arterioles

each supply one nephron, leads to a ball of capillaries=glomerulus

What is blood drained from glomerulus by?

efferent arterioles

What do most efferent arterioles lead to?

peritubular capillaries

What do some or the minority of efferent arterioles lead to?

vasa recta

Vasa recta

 network of blood vessels within renal medulla

Where do peritubular and capillaries and vasa recta lead to?

cortical radiate veins or directly into arcuate veins

what do arcuate veins lead into?

interlobar veins

What do interlobar veins lead into?

renal vein

Where does renal vein empty into?

inferior vena cava

Blood flow through kidneys

aorta, renal artery, segmental artery, interlobar artery, arcuate artery, cortical radiate artery, afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries or vasa recta, cortical radiate vein, arcuate vein, interlobar vein, renal vein, inferior vena cava

What supplies the tissue near the glomerulus?

convoluted peritubular capillaries

What supplies nephron loop portion of the nephron?

vasa recta in the medulla

Two parts of nephrons

renal corpuscle and renal tubule

Renal corpuscle of nephron

filters blood plasma

renal tubule of nephron

long, coiled tube that converts the filtrate into urine

What does renal corpuscle consist of?

glomerulus and a two-layered glomerular capsule that encloses glomerulus

What type of tissue is parietal layer of the glomerular capsule?

simple squamous epithelium

What does the visceral layer of glomerular capsule contain?

podocytes that wrap around the capillaries of the glomerulus

What separates the two layers of the glomerular capsule?

capsular space-where filtrate builds up

Vascular pole

the side of the corpuscle where the afferent arterial enters the corpuscle and the efferent arteriole leaves

urinary pole

the opposite side of the corpuscle where the renal tubule begins

Renal tubule

duct leading away from the glomerular capsule and ending at the tip of the medullary pyramid

What are the four regions of the renal tubule?

Proximal convoluted tubule, nephron loop, distal convoluted tubule, collecting duct

What does collecting duct receive fluid from?

many nephrons

Proximal convoluted tubule

arises from glomerular capsule, Longest and most coiled region

What type of epithelial tissue is proximal convoluted tubule?

Simple cuboidal epithelium with prominent microvilli for majority of absorption

Nephron loop

 long U-shaped portion of renal tubule, Descending limb and ascending limb

Thick segments of nephron loop

have simple cuboidal epithelium, Initial part of descending limb and part or all of ascending limb, heavily engaged in the active transport of salts and have many mitochondria

thin segment of nephron loop

has simple squamous epithelium, Forms lower part of descending limb, Cells very permeable to water

Distal convoluted tubule

begins shortly after the ascending limb reenters the cortex, Shorter and less coiled than PCT, Cuboidal epithelium without microvilli, DCT is the end of the nephron

Collecting duct

 receives fluid from the DCTs of several nephrons as it passes back into the medulla, Numerous collecting ducts converge toward the tip of the medullary pyramid

Papillary duct

formed by merger of several collecting ducts, 30 papillary ducts end in the tip of each papilla, Collecting and papillary ducts lined with simple cuboidal epithelium

Pathway of filtrate flow

glomerular capsule → proximal convoluted tubule → nephron loop → distal convoluted tubule → collecting duct → papillary duct → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra

Juxtamedullary nephrons

very long nephron loops, maintain salinity gradient in medulla, help conserve water

Cortical nephrons

more numerous, short nephron loops

Renal plexus

nerves and ganglia wrapped around each renal artery, issues nerve fibers to blood vessels and convoluted tubules of the nephron

What is the renal plexus important for?

fluid balance and blood pressure regulation

What does renal innervation carry?

sympathetic innervation from the abdominal aortic plexus

What does stimulation of sympathetic innervation do?

reduces glomerular blood flow and rate of urine production

What happens to nephron activity during dehydration?

nephron activity gets readjusted from cortical nephrons to juxtamedullary nephrons

Glomerular filtrate

fluid in the capsular space, very similar to blood plasma except it has no proteins, very dilute

Tubular filtrate

fluid from the proximal convoluted tubule to the distal convoluted tubule, substances have been removed or added by tubular cells, less dilute, still being chemically processed

Urine

fluid that leaves the collecting ducts, undergoes little alteration in collecting duct except for changes in water content

What are the four stages that the Kidneys have to convert blood plasma into urine?

Glomerular filtration, tubular reabsorption, tubular secretion, water conservation

What happens to urine output if blood flow through the nephrons increases?

it also increases

Glomerular filtration

capillary fluid exchange where water and some solutes pass from the capillaries of the glomerulus into capsular space of the nephron, creates a plasma like filtrate of the blood

What are the three membranes of the filtration membrane?

Fenestrated endothelium, basement membrane, filtration slits

Which filtration membrane does the most filtration and why?

The basement membrane, has the smallest gaps, and has a negative charge that repels albumin, so it is electrostatically and regularly filtering membranes

Filtration slits

podocyte cell extensions wrap around capillaries to form a barrier layer, also negatively charged

What type of molecules can make it through the filtration membrane?

any smaller molecules like Water, electrolytes, glucose, fatty acids, amino acids, nitrogenous wastes, ATP (if in blood plasma), and vitamins, pretty much any small molecule that is not bound to a protein

Proteinuria

presence of protein in urine

Hematuria

presence of blood in the urine

What is a common cause of hematuria and proteinuria?

prolonged strenuous exercise because it reduces perfusion of the kidneys

What does filtration pressure depend on?

hydrostatic and osmotic pressure on each side of filtration membrane

Blood hydrostatic pressure

high in glomerular capillaries because the afferent arteriole is larger than the efferent arteriole

Colloid osmotic pressure in glomerular filtrate

little to none because glomerular filtrate has no proteins, higher outward pressure opposed by two inward pressures

What does high blood pressure in glomerulus make kidneys vulnerable to?

Hypertension, which can lead to rupture of the glomerular capillaries

What is the glomerular filtration rate?

amount of filtrate formed per minute by the two kidneys combined, is a very high amount

What happens to the majority of the filtrate that we produce?

most of it is reabsorbed otherwise we would urinate WAY more than we actually do