Urinary system Flashcards
Urinary system components
Kidneys (2)
Ureters (2)
Bladder
Urethra
Anatomy & function - Kidneys - location and main role
Main (2) organs within urinary system; reddish, bean shaped organs which are retroperitoneal (retro – behind, peritoneal – peritoneum).
They sit within abdominal cavity, below diaphragm, at back of abdomen and are partially protected by the 11th & 12th ribs (between vertebral T11-L3).
The right kidney is lower due to the liver space.
The kidneys perform the major functions of the urinary system and secrete urine into ureters (they filter blood and decide what to excrete / reabsorb)
Anatomy & function; Kidney layers
Each kidney is surrounded by three layers:
Renal capsule (deep /innermost)
Adipose capsule (middle)
Renal fascia (superficial /outer)
- Renal capsule (deep / innermost layer): Smooth, transparent sheet of connective tissue. Maintains kidney shape
- Adipose capsule (middle layer): Mass of fatty tissue, providing protection and support
- Renal fascia (superficial layer): Thin layer of connective tissue that anchors kidneys to surrounding structures.
Anatomy & function; Kidney regions
The kidney is divided into 2 distinct regions;
- Renal cortex (cortex = bark (tree) e.g outside)–superficial, light red area
- Renal medulla – darker area composed of several cone-shaped structures called renal pyramids (locations that accumulate urine that has been formed)
Anatomy & function; Hilum
Hilum; On the concave kidney border. The region where blood vessels, lymph vessels, nerves and ureters enter and exit the kidney
Kidney blood supply and cardiac output
Blood supply;
Renal artery supplies blood to the kidneys from the heart.
Renal vein drains blood from the kidneys.
The kidneys receive 20-25% of the cardiac output (1.2L blood per minute), despite its mass accounting for 0.5% of body weight
Urinary system Functions
Excretion of unwanted substances
Maintenance of water & electrolyte balance
pH regulation of body fluids (esp. the blood)
Production of hormones (erythropoietin & calcitriol)
Regulation of red blood cells (erythrocyte) production
Regulation of blood glucose levels
Regulation of blood pressure, volume & osmolarity
Urinary system functions; Excretion
Include Metabolic wastes, Ions and Toxins:
- Metabolic wastes (All contain nitrogen; the kidneys specialise in removing nitrogenous waste):
Urea; a metabolite of protein metabolism
Uric acid; product of purine metabolism
Creatinine; An end product of muscle metabolism - Ions:
In particular Hydrogen (H+) – Acidic - Toxins:
Medications, toxins and deactivated hormones are mostly detoxified in the liver and then excreted via the kidneys.
Urinary system functions; water balance
Water balance:
The body’s water balance is mainly controlled by the kidneys
Minimum urine content required to clear body waste is 500ml/day
The feedback mechanism may be altered in pathologies; e.g. untreated diabetes mellitus
Urinary system functions; electrolyte balance
Electrolyte balance:
Electrolytes are charged atoms in solution (they can conduct electricity)
The most important electrolytes regulated by the kidneys are;
Sodium (Na+) (regulates blood volume)
Potassium (K+) (nervous system)
Hydrogen (H+) (acidic)
Electrolytes can form buffer substances. These are molecules that can buffer / regulate changes in pH.
An excess of H+ ions is an acidic solution. If a buffer is present it can bind with the free H+ ions thus resisting a change in pH (resisting an increase in H+ ions)
Urinary system functions; pH regulation
pH balance:
Blood pH must remain fairly constant – 7.35 – 7.45
There are two primary pH control systems:
1. Lungs excrete CO2 (the more CO2 in blood = more acidic)
- Kidneys; Excrete H+ into urine and produce the buffer HCO3 (bicarbonate)
Urinary system functions; hormone production - calcitriol
Calcitriol:
Calcitriol = active form of Vitamin D
UV light activates a Vit. D precursor in skin. Kidneys convert inactive vit. D into its active form
It increases bone formation (increases calcium):
- Stimulates calcium & magnesium uptake from GIT
- Reduces calcium loss in kidneys (along with PTH)
A deficiency can cause rickets and osteomalacia
Urinary system functions; hormone production - RBC regulation / production - erythropoietin
Erythropoietin:
A protein hormone that is secreted by the kidneys into blood (10% produced in liver), that stimulates erythropoiesis (red blood cell synthesis) in the red bone marrow.
Released in response to hypoxia (negative feedback)
In renal failure, erythropoietin production is inadequate and hence results in anaemia
Can be measured on blood test (EPO test)
(erythro = red (blood cell), poietin = a growth promoting agent, poiesis = formation, hypo = low, oxia = oxygen)
Urinary system functions; blood sugar regulation
The normal blood glucose level is 4-7 mmol/L
Hyperglycaemia: The renal threshold for glucose is 9mmol/L. Above this level (in blood), glucose cannot be reabsorbed from nephrons into the blood when passing through kidney tubules
Hyperglycaemia indicates pathology; e.g. diabetes mellitus
Hypoglycaemia: The kidneys are able to make glucose from the amino acid glutamine to help elevate blood sugar levels when hypoglycemic – gluconeogenesis
(hyper = elevated, hypo = low, glycaemia = blood sugar, gluco = glucose, -neogenesis = new formation)
Urinary system functions; blood volume, pressure & concentration
- Conserving or eliminating water in urine
- Regulating the loss of solute in the urine which helps to maintain a constant blood concentration / osmolality
- The kidneys help to regulate blood pressure by secreting the enzyme renin, which activates the Renin-Angiotensin-Aldosterone pathway. Increased renin causes an increase in blood pressure
More water excreted = lowers BP
Less water excreted (more conserved in blood) = raises BP
(solute = substances dissolved in a liquid)
Anatomy and functions; Nephron - parts
The functional unit of the kidney. More than one million per kidney. Single epithelial layer.
Parts inc;
Glomerulus
Bowmans’ capsule
Proximal convoluted tubule (PCT)
Loop of Henle (aka nephron loop)
Distal convoluted tubules (DCT) Collecting duct
Afferent arteriole & Efferent arteriole
Peritubular capillaries
(Convoluted = twisted, anti = against, diuresis = urination)
Anatomy and functions; Nephron - two main functional parts
Consists of two main functional parts;
1. Renal corpuscle (Bowmans capsule & glomerulus)
2. Renal Tubule (proximal & distal convoluted tubules)
The renal corpuscle and both convoluted tubules are located in the renal cortex (outer area of kidney).
The renal pyramids consist of collecting ducts and loops of henle (apex)
Anatomy and functions; Nephron - renal corpuscle
Renal Corpuscle;
Consists of glomerulus and Bowman’s capsule.
The glomerulus is a capillary network (very permeable) that receives blood from afferent arteriole to filter (blood Exits through Efferent arteriole).
The Bowman’s capsule is a double walled capsule that surrounds the glomerulus, receiving contents of filtered blood.
Anatomy and functions; Nephron - renal tubule
Renal Tubule;
Consists of 3 sections;
Proximal convoluted tubule (PCT)
Loop of Henle
Distal convoluted tubule (DCT)
Filtered fluid is passed through the tubule.
Important role in reabsorption & secretion of various solutes.
Antidiuretic hormone (ADH) acts on the distal convoluted tubule to reabsorb water
Anatomy and functions; renal
Pelvis
A funnel shaped tube surrounded by smooth muscle that uses peristalsis to move urine out of the kidney, into the ureter, and to the bladder
Anatomy and functions; Ureters
The two ureters transport urine from the renal pelvis to the urinary bladder.
Each ureter is approx. 25-30cm and is retroperitoneal.
Peristaltic contractions of the muscle wall (aided by gravity and urine pressure) propel urine towards bladder.
A valve prevents backflow.
Anatomy and functions; Ureter tissue layers
Three layers of tissue form the walls of the ureters:
- Inner mucous membrane; Contains transitional epithelium (stretchy). Also contains goblet cells – secrete mucus for protection from urine.
- Muscularis; Consists of smooth muscle fibres which produce peristaltic contractions
- Adventitia; An outer coat of connective tissue that contains blood & lymph vessels, as well as nerves
Anatomy and functions; Urinary bladder
A hollow, muscular organ that acts as a reservoir for urine.
Becomes spherical as it fills, and collapses when empty. Folds of peritoneum (rugae) hold it in position.
Anatomy and functions; Urinary bladder tissue layers
Composed of three layers of tissues:
- Inner mucosal layer; Transitional epithelium supported by connective tissue. The mucosa folds to permit expansion
- Muscularis; AKA the detrusor muscle (smooth). Smooth muscle fibres accumulate at the urethral opening and form the internal urethral sphincter (involuntary)
- Adventitia: Outer layer of connective tissue
Anatomy and functions; Urethra
The urethra is the tube leading from the bladder to the exterior of the body (passageway for discharging urine).
Between the internal urethral sphincter (involuntary) and external urethral sphincter (voluntary)
Female urethra is 4cm whilst male is 20cm (male approx. 5 x longer)
Male urethra divided into 3 portions; prostatic, membranous & spongy. The male urethra passes through the prostate where it receives semen during ejaculation
Urine formation (3 processes):
To produce urine, the nephrons and collecting ducts perform three basic processes:
1) Glomerular filtration: Occurs in the renal corpuscle
2) Tubular reabsorption; occurs in the renal tubules
3) Tubular secretion; occurs in the renal tubules
Urine filtration; glomerular filtration
Glomerular capillaries present a large surface area for filtration.
Water and small molecules pass through pores in the capillaries into the Bowman’s capsule
Larger molecules (e.g. plasma proteins, blood cells) are unable to filter through because of the size of the pores (they reside in the blood)
Urine filtration; glomerular filtration adapted structure
Glomerular filtration is adapted for filtration by:
1) The diameter of efferent arteriole (exit) is less than that of the afferent arterioles = high pressure in the glomerulus)
2) Glomerular capillaries are ~50x leakier than normal capillaries
