renal physiology

Functions of the urinary system

1. Filters and excretes waste products from the blood

2. maintaining homeostasis pf blood composition
   3. Regulating blood pH (hydrogen and bicarbonate)
   4. Hormone and enzyme production (kidneys)
   5. Maintain blood volume homeostasis
   6. Regulating blood pressure
   7. Regulates blood osmolarity
   

Micturition Reflex

As the volume of the bladder increase (>200-400 mL), stretching of the bladder walls send signals to the CNS.

Blood flow through the kidneys

There is one afferent glomerular arteriole per nephron.

Functional unit of the kidneys

Where the ureter and blood vessels exit (~1 million per kidney).

Transport and storage of urine

Urine is transported to the bladder for storage via the ureters until it exits the body via the urethra.

Main structures of the urinary system

Blood filtration occurs in the kidneys to produce urine.

Nephron

The functional unit of the kidney responsible for filtering blood and forming urine.

Renal corpuscle

The part of the nephron that filters blood, consisting of the glomerulus and Bowman's capsule.

Bowman's capsule

Also known as the glomerular capsule, it surrounds the glomerulus and collects the filtrate.

Glomerulus

A network of capillaries located within the Bowman's capsule where blood filtration occurs.

Renal tubule

The part of the nephron that processes the filtrate after it leaves the renal corpuscle.

PCT

Proximal convoluted tubule, the first segment of the renal tubule where reabsorption occurs.

Nephron loop

Also known as the Loop of Henle, it is the U-shaped segment of the renal tubule.

DCT

Distal convoluted tubule, the segment of the renal tubule that follows the nephron loop.

Collecting ducts

Structures that receive filtrate from multiple DCTs and transport it to the papillary ducts.

Papillary duct

The duct that collects urine from the collecting ducts and drains it into the renal pelvis.

Cortical nephrons

Nephrons that make up 80-85% of all nephrons, characterized by shorter nephron loops.

Juxtamedullary nephrons

Nephrons that make up 15-20% of all nephrons, characterized by longer nephron loops extending deep into the renal medulla.

Glomerular filtration pressure

The blood pressure in the capillaries that drives the filtration of blood in the glomerulus.

Glomerular filtration rate

The quantity of filtrate produced per minute, typically ~105 - 125 mL/minute.

Daily glomerular filtrate production

Approximately 150 - 180 L of glomerular filtrate is created per day.

Urine production

Typically ~1 - 2 L of urine is produced per day after >99% of filtrate is reabsorbed.

Filtration rate regulation

Filtration rate is regulated by controlling glomerular blood flow and the surface area of the glomerulus.

Leaky glomerular filtration membrane

A membrane that allows small solutes and water to pass through during filtration.

Blood proteins

Substances that resist filtration in the glomerulus.

Thin segment of nephron loop

A part of the ascending limb of the nephron loop characterized by thinner epithelial cells.

Thick segment of nephron loop

A part of the ascending limb of the nephron loop characterized by thicker epithelial cells.

Tubular reabsorption

Substances move back into the blood from the nephron.

Tubular secretion

Substances move from the blood into the nephron.

Obligatory water reabsorption

Water follows the solutes back into the blood through osmosis, accounting for 80% of water reabsorption.

Facultative water reabsorption

The remainder of water reabsorption occurs in the late distal tubule and the collecting duct and is facilitated by antidiuretic hormone, accounting for 20% of water reabsorption.

Reabsorption in the PCT

The PCT will reabsorb 50% of the chlorine ions and urea, 65% of the water, sodium ions, potassium ions, and calcium ions, 80% of the bicarbonate ions, and 100% of the glucose and amino acids.

Sodium symporters

A primary mechanism for solute reabsorption in the PCT that involves the co-transport of sodium with other solutes.

Sodium hydrogen antiporters

Transporters in the PCT that exchange sodium ions for hydrogen ions, facilitating the secretion of hydrogen ions.

Passive transport of solutes in the PCT

As water moves into the blood, it concentrates the tubular fluid, which facilitates the passive transport of solutes into the blood as they move down their concentration gradient.

Disposal of ammonia and urea

During the breakdown of amino acids within the liver cells, a by-product created is ammonia.

Solutes secreted in tubular secretion

Creatine, hydrogen ions, urea, and ammonium ions are secreted into the tubular fluid.

Solutes reabsorbed in tubular reabsorption

Glucose, amino acids, ions (sodium, calcium, potassium, phosphate, chloride, bicarbonate), and urea are reabsorbed.

Antidiuretic hormone

A hormone that facilitates facultative water reabsorption in the late distal tubule and collecting duct.

Percentage of water reabsorption

80% of water reabsorption is obligatory, while 20% is facultative.

Mechanisms regulating reabsorption

Transporters and hormones such as sodium symporters, antiporters, and antidiuretic hormone regulate and facilitate reabsorption.

Role of kidneys

The kidneys play a crucial role in blood volume and blood pressure regulation.

Fluid passage through nephron

The reabsorption process is fine-tuned as fluid passes through different regions of the nephron.

Concentration gradient

The difference in concentration of solutes that drives the passive transport of solutes in the nephron.

Filtrate

The fluid that is filtered through the nephron, from which substances are reabsorbed or secreted.

Sodium ions

Ions that are reabsorbed in significant quantities in the PCT and play a crucial role in solute transport.

Chlorine ions

Ions that are reabsorbed in the PCT, with 50% being reabsorbed from the filtrate.

Urea

A waste product that is both reabsorbed and secreted in the nephron.

Ammonia

A toxic substance that is converted into urea by liver cells.

PCT (Proximal Convoluted Tubule)

The segment of the nephron where substances are secreted into the tubular fluid.

Bicarbonate Ions Reabsorption

10% of bicarbonate ions are reabsorbed in the nephron loop.

Water Reabsorption in Nephron Loop

15% of water is reabsorbed in the nephron loop.

Sodium, Potassium, and Calcium Ions Reabsorption

25% of sodium, potassium, and calcium ions are reabsorbed in the nephron loop.

Chloride Ions Reabsorption

35% of chloride ions are reabsorbed in the nephron loop.

Magnesium Ions

Magnesium ions are reabsorbed in the nephron loop without set quantities.

Descending Limb of Nephron Loop

Responsible for water reabsorption in the nephron loop.

Ascending Limb of Nephron Loop

Very minimal water is reabsorbed here due to low permeability to water.

Na+ - K+ - 2Cl- Symporters

Transporters in the thick segment of the ascending limb that move 1 Na+, 1 K+, and 2 Cl- into the blood.

Early DCT (Distal Convoluted Tubule)

Reabsorbs 5% of sodium and chloride ions and calcium ions stimulated by parathyroid hormone.

Na+ - Cl- Symporters in Early DCT

Facilitate ionic reabsorption into the blood in the early DCT.

Later DCT

Allows for fine-tuned reabsorption and secretion to promote homeostasis after 90-95% of water and solutes have been reabsorbed.

Hormonal Regulation of Reabsorption

Key hormones include Angiotensin II, Aldosterone, Antidiuretic hormone, Atrial natriuretic hormone, and Parathyroid hormone.

BV + BP

Refers to blood volume plus blood pressure.

Filtration in the Kidney

The process by which blood is filtered in the glomerulus.

Reabsorption in the Kidney

The process of reclaiming water and solutes from the tubular fluid back into the blood.

Secretion in the Kidney

The process of adding substances from the blood into the tubular fluid.

main structures of the urinary system

• right kidney

• right ureter

• urinary bladder

• urethra

• left kidney

• left ureter

where does blood filtration occur

in the kidneys which produce urine

what is the order of transport for urine

1. bladder for storage through the ureters

2. exits body through the urethra

urethra sex based differences

• urethra is five times longer in males than females

• urethra is divided into sections for males but is one short tube for females

• urethra is used for urine and genital systems in males and the two systems are separate in females

micturition reflex

• As the volume of the bladder increase (>200-400 mL),stretching of the bladder walls send signals to the CNS

• The reflex output results in the detrusor muscles of the bladder contracting and the internal urethral sphincter relaxing.

• In order to empty the bladder, the external urethral sphincter must also relax, which can be consciously and voluntarily controlled at the level of the cerebral cortex (learned).

hilum of the kidney

where the ureter and blood vessels exit the kidney

blood flow through kidneys order

renal artery

segmental arteries

interlobar arteries

arcuate arteries

cortical radiate arteries

afferent glomerular arterioles

glomerular capillaries

efferent glomerular arterioles

peritubular capillaries

peritubular venules

cortical radiate veins

arcuate veins

interlobar veins

real vein

blood flow through kidneys

• there is one afferent glomerular arteriole per nephron

• glomerulus = ball of glomerular capillaries

nephron structure

1. renal corpuscle

• glomerular capsule = goes towards the bowman's capsule