Anatomy Unit 4

The four basic functions of the kidneys

Excretory: creation and concentration of water-soluble waste

Endocrine: secretion of response to humans

Cardiovascular: regulation of blood pressure

Respiratory: removal of dissolved gases

Retroperitoneal

kidneys are situated behind the peritoneum in the abdominal cavity

Ureters

transport urine from kidneys to the bladder

Bladder

holds urine

Urethra

Transports urine out of the body

Protective structures of the kidney

Anterior: viscera of the abdomen

Posterior: ribs 11&12; inferior protection=quatratus lumborum

Three locations where kidney stones are commonly lodged

Narrow part of the ureter, going over the common iliac, entering the back of the bladder

Nervous system control of the urethral sphincters

Internal: smooth muscle and involuntary

External: skeletal muscles and voluntary

Micturition

Excretion of urine from bladder to urethra

Nervous system control of micturition

Parasympathetic impulses cause detrusor muscle to contract and internal/external sphincters to relax, allowing urination.

Sacral spinal reflex pathway of micturition

1. stretch receptors in mucosa of the bladder send signals to the sacral region of spinal cord

2. Reflexive response from the spinal cord causes relaxation of the internal urethral sphincter (smooth muscle)

3. Somatic response from the CNS travels down the spinal cord & causes relaxation of the external urethral sphincter (skeletal muscle)

Describe the goal of toilet training

Since the external sphincter is under voluntary control, toilet training is aimed at learning to control this muscle in order to maintain urinary continence

Clinical relevance if the difference in urethra length in males vs females

Males: more likely to get injured from catheter (20cm)

Females: more likely to get a UTI (4-6cm)

Urethral segments in the male

1. prostatic urethra: runs through prostate

2. Membranous urethra: runs through CT membrane

3. Penile urethra: runs through the penis

Structures that pass through hilum of the kidney

Ureter, nerves, blood vessels & lymphatic vessels

3 layers that surround the kidney

1. Renal fascia: superficial

2. Adipose capsule: middle

3. Renal capsule: deep

Pathway of urine from renal papillae to bladder

1. Renal papillae

2. Minor calyx

3. Major calyx

4. renal pelvis

5. ureter

6. bladder

Renal blood supply pattern

1. Aorta

2. Renal artery

3. Segmental artery

4. Interlobar artery

5. Arcuate artery

6. Corticol artery

7. Afferent arterioles

8. Glomerular capillaries

9. Efferent arterioles

Afferent arteriole

delivers blood to glomerulus

Glomerulus

Filtration of the blood

Efferent arteriole

carries blood away from the glomerulus

Peritubular capillaries

Regas and nutrient exchange

Functional unit of the kidney

Nephron

Nephron

responsible for filtering blood and producing urine.

3 principal actions of the nephron

1. glomerular filtration: substances move from the blood into the glomerulus to produce the initial filtrate

2. Tubular reabsorption: fluid & solutes are reabsorbed from the filtrate, returning to the blood

3. Tubular secretion: substances move from the blood into the filtrate

Proteins

never get filtered from blood to nephron

Glucose

always gets filtered and reabsorbed

Cortical nephrons

corpuscles in outer cortex, short nephron loop, 80-85% of human nephrons, supplied by peritubular capillaries

Juxtamedullary nephrons

corpuscles located near the medulla, long nephron loop, 15-20% of human nephrons, good for H2O retention, supplied by unique capillaries called the vasa recta

Glomerular capsule: filtration of the blood

simple squamous epithelium: diffusion of membrane

podocytes: prevent blood protein filtration

mesangial cells: removes filtered debris

Proximal convoluted tubule: reabsorption of water and nutrients

Cuboidal cells with brush border: absorption (tubular secretion)

Descending nephron loop: reabsorption of water from the filtrate

Simple squamous: diffusion and H2O exchange

Ascending nephron loop: reabsorption of Na+ and Cl- ions from the filtrate

Cuboidal to columnar: salt exchange

Juxtaglomerular apparatus

Macula densa cells: detect salt concentration and blood pressure

Juxtaglomerular cells: on afferent arteriole and adjust vessel diameter

Distal convoluted tubule: secretion and reabsorption of ions to maintain blood pH and electrolyte balance and collecting duct: reabsorbs solutes & water from the filtrate to produce the final urine product

Principal cells with intercalated discs: help adjust salt and H2O content of urine, modulate pH

Process of filtrate production

1. Filtration occurs in the glomerulus of the kidney

2. Blood enters the glomerulus via the afferent arteriole

3. Water, ions, and waste are filtered out of the blood within the glomerular capillaries into the renal tubule.

4. The fluid in the nephron is the filtrate

5. The remaining blood leaves the glomerular capillaries via the efferent arteriole.

Blood hydrostatic

pressure of blood/plasma against glomerular wall

Blood osmotic

pressure that plasma/filtrate exerts on the capsule wall

Capsular hydrostatic

pressure of tubular fluid against walls of capsule

Change in diameter changes filtration in the glomerulus

Vasodilation allows for more blood flow to glomerulus which increases pressure and filtration rate

Vasoconstriction decreases blood flow and decreases blood pressure and filtration

3 elements of glomerular membrane that control filtration

1. glomerular endothelial cells: large pores

2. basal lamina: basement membrane

3. Podocytes: thin filtration slits

Should be in the urine

Ions, protons, urea, some hormones

Should not be in urine

glucose, insulin, cholesterol, CO2, blood, ketones, bile pigments, proteins

3 features that allow for filtration in the glomerulus

high surface area, fenestrated endothelium, high capillary pressure

Glomerular filtration rate

the amount of blood filtered per minute

3 mechanisms of control of GFR

1. renal auto-regulation

2. Neural regulation

3. Hormonal regulation

RAAS

increases blood pressure of vasoconstriction

angiotensinogen 1 to 2

ADH

increases blood pressure by reabsorbing water

ANP

decreases blood pressure by inhibiting reninand promoting the excretion of sodium.

Steps of RAAS

1. BP/GFR decreases

2. JG cells release renin

3. Renin carries angiotensinogen to angiotensin 1

4. ACE converts angiotensin-1 to active angiatensin-2

5. promotes vasoconstriction of efferent arterioles and systemic blood vessels

6. Promotes reabsorption of Na and Cl from proximal tubule and H2O follows, reabsorbs salt and targets adrenal gland

7. promotes aldosterone release, leading to increase Na and H2O reabsorption

8. Stimulates thirst center in hypothalamus may increase fluid intake

Relationship between blood volume and pressue

directly related: more blood volume=more blood pressure

Relationship between CO2 and pH in the blood

Inversely related: more CO2=lower pH (acidic)

Maintain the homeostasis of pH in the blood

Too low (acidic): reabsorption of bicarbonate in PCT and secretion of H+ ions in the DCT and collecting duct

Too basic: decrease reabsorption of bicarbonate, decrease secretion of H+ ions

Process of production of urine

Reabsorption: into blood from filtrate

Secretes: into filtrate from blood

PCT: reabosrbs water, glucose, amino acids, ions. secretes H+, wastes like uric acid

Descending limb: reabsorbs water, secretes nothing

Ascending limb: reabsorbs salts, secretes nothing

DCT: reabsorbs water,ions, secretes ions

Collecting duct: reabsorbs water, Na+, Cl-, secretes H+

Key elements of the countercurrent flow

Aorta, renal artery, afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries, vasa recta

Glomerular capsule, PCT, descending limb, ascending limb, DCT, collecting duct, minor calyx, major calyx, renal pelvis, ureter, bladder urethra