Urinary system

urinary system functions

• Excretion: filters waste product from blood in the form of urine

• regulation: Blood volume and pressure, Blood solute concentration

• Red blood cell and vitamin d synthesis

• Extracellular fluid pH

• Erythropoietin

kidneys

Filter blood and eliminate waste via urine

ureter

Thin tubes that carry urine from kidneys to the bladder

Urinary bladder

• Stores urine, muscles expand to hold urine

• contains transitional epithelium which allows it to stretch and relax

urethra

Tube which carries urine from the bladder out of your body

renal capsule

• innermost kidney layer

• transparent membrane, fibrous coating, maintains organ shape

adipose capsule

helps protect from trauma

renal fascia

• outermost kidney layer

• dense, irregular connective tissue that holds against back body wall

renal pelvis

• funnel shaped located in the innermost part of kidney

• allows for a pathway for fluid on its way to the bladder

• first portion of the ureter in the kidney

minor calyx

• urine is filtered here before the major calyx

• drains into major calyx

• located at the apex of the renal papilla

major calyx

bigger funnel where urine is filtered into

hilum

• entry region for renal artery and nerve

• contains an area called the renal sinus

renal sinus

minor, major renal vein, ureter, and lymphatic vessels pass through here before exiting kidney at the hilum region

renal cortex

• outer layer of the kidney located btwn the renal capsule and renal medulla

• Contains the glomerulus and renal convoluted tubules

renal medulla

Inner tissue of the kidney and contains the loop of Henle and renal pyramids

renal pyramids

collection of tubes and ducts which transport fluids throughout the kidneys

renal papilla

point toward center of kidney

nephron

• Functional unit of the kidney

• approx. 1.3 million in each kidney

• Separates water, sodium chloride, potassium, AA, glucose, creating, urea, and bicarbonate

Glomerulus filtration

a portion of the blood plasma is filtered into the kidney nephrons

tubular reabsorption

water & useful substances are reabsorbed back into the blood

tubular secretion

Further wastes are removed from the blood & secreted into urine

excretion

urine out of the nephron via the collecting tube

renal tubules

Tiny tubes within each kidney which returns nutrients, fluid back to the blood, and the rest is excreted in the form of urine

Afferent arterioles

blood to the glomerulus

Efferent arterioles

Blood away from the glomerulus

Proximal convoluted tubule

• water, potassium, glucose, amino acid and bicarbonate are reabsorbed in this area

• Uric acid is secreted into this tubule

Nephron loop

concentration of urine: reabsorbing water in the descending limb, and reabsorbing sodium chloride in ascending limb

Distal convoluted tubule

• reabsorb some filtered sodium chloride and water

• also some potassium and hydrogen ions are secreted into the nephron (fine tuning)

Collecting tubule/duct

• takes urine from the distal convoluted tubule into the renal papillae and out of the kidney (water)

• not part of the nephron

juxtamedullary

• Make up 15% of nephrons; Found deep in the cortex of the medulla

• Functions in concentrating/diluting urea

• Contains bowman’s capsule, proximal convoluted tubule, long loops of henle, distal convoluted tubule and collecting duct

cortical nephrons

• Make up about 85% of nephrons

• Performs excretory and regulatory functions of the kidney

• Contains bowman’s capsule, proximal convoluted tubule, shorter loops of henle, distal convoluted tubule and collecting duct

renal corpuscle

• Filtration portion

• made of: Mesangial cells, Glomerulus, Bowman capsule

Mesangial cells

• Provide structural support to the glomerulus so the capillaries are not free floating

• Inflammatory and immunity

Glomerulus

• Network of capillaries

• High pressure of blood flow

Bowman capsule

• Chamber which surrounds the glomerulus

• Filters fluid

• made of: Outer parietal layer, Inner visceral layer

Juxtaglomerular apparatus

Contains unique sets of afferent arterioles and cells within the distal convolute tubules

Juxtaglomerular cells

• smooth muscles cells where the afferent arteriole enters the renal corpuscle

• Stores, synthesize and secrete renin

renin

promotes the production of angiotensin

Angiotensin

regulates blood pressure by narrowing BV and water/salt intake

Macula densa

maintain body fluid, sodium and BP, cells found within the walls of the distal convoluted tubules

glomerular filtrate

• fluid that enters the bowman’s capsule

• No cells, no proteins

• 1% gets pushed into the nephron to filter as urine

• Less than 1.8nm is filtered through; More than 3.6nm is not filtered through

Fenestration

slits/holes in the glomerulus which prevents certain molecules to get through

Basement membrane

• Contains collagen which has a negative charge

• Prevents proteins (negative charge) from filtrating through

Podocytes

• Provide structural support, but are cells

• Stops medium-sized proteins, not small ones

glomerular filtration rate

• Amount of filtrate formed in all bowman’s of both kidneys per minute

• 20% of blood enters the kidney (1000ml;1L)

• 600ml enter glomerulus to be filtered out, 20% filtered into bowman’s capsule; 120-125ml per minute filtered into bowman’s capsule

• 173-175L filtered directly into nephron per day

• Urinate out about 1.7 L

Intrinsic mechanism

• within the kidneys; Maintains GFR constant

• Mechanisms that maintain a constant GFR despite changes in arterial BP

myogenic mechanism

systemic increases and decreases in BP

Systemic decrease in BP

• smooth muscle contraction reduces the diameter of the afferent arterioles (dilate)

• dilation of the afferent arterioles, increases GFR and increases urine output

systemic increases in BP

• smooth muscle contraction stretch the afferent arteriole & cause an increase GFR

• constrict afferent arterioles, decreasing GFR and urine output

Tubuloglomerular feedback

achieved by macula densa that detects the changes in salt concentration which controls cells to release a vasoconstrictor from the juxtaglomerular apparatus

Extrinsic control

• Maintains BP

• Really high or really low arterioles pressure

Neural control

• Baroreceptor reflex

• BP increases above normal range which detects the increase the pressure and send action potential; increase parasympathetic and decrease sympathetic: results in decreased heart, and dilation of arterioles which decreases BP

• BP decreases below normal range, send fewer action potential, medulla increase sympathetic and decrease parasympathetic division: results in increase heart rate, increase constriction

Hormonal control

Renin-angiotensin: angiotensin is converted to angiotensin II when renin is released

Angiotensin II

• causes constriction of arteriolar

• stimulates reabsorption of sodium by releasing aldosterone (increase sodium reabsorption), the hypothalamus release of ADH (control water and salt absorption, and constrict BV), and increase thirst

Urine

about 95% water and 5% waste (urea, creatine, ammonia and uric acids, sodium, potassium, hydrogen, calcium)

urine flow

Nephrons → collecting duct/tube → renal papillae → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra → secreted out of the body

Urination

• Also referred to as Micturition Reflex

• Coordinated by neurons from the brain and sacral region

• Autonomic reflex

internal sphincter

involuntary; surrounds opening of the bladder to the urethra and relaxes to allow urine to pass

External sphincter

voluntary; surrounds the urethra outside the bladder and must be relaxed for urination to happen

stretch receptors

• send impulse to the sacral region

• stimulates the muscle of the bladder along with the relaxation of the internal sphincter

• send message to the thalamus and cortex to initiate voluntary control over the external sphincter of the urethra