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
Urine filtration; glomerular filtration - pressure types
Glomerular filtration depends on 3 main filtration pressures:
1) Blood pressure
2) Blood colloid osmotic pressure
3) Capsular hydrostatic pressure
Urine filtration; glomerular filtration - pressure - blood pressure
Blood pressure in the glomerular capillaries; promotes filtration by forcing substances through the membrane
Urine filtration; glomerular filtration - pressure - blood colloid osmotic pressure
Blood colloid osmotic pressure; proteins present in blood plasma (i.e. albumin, globulins, fibrinogen) within the glomerular capillaries oppose filtration
Urine filtration; glomerular filtration - pressure - capsular hydrostatic pressure
Capsular hydrostatic pressure; back pressure of the fluid that has already filtered through opposes filtration
Urine filtration; glomerular filtration rate (GFR)
The amount of filtrate formed in the renal corpuscles of both kidneys each minute.
In adults, the GFR averages 125ml/min (M) and 105ml/min (F). A normal GFR should be over 90ml/min
The rate needs to be constant for homeostasis.
GFR is calculated through a blood test and the result determines the severity of kidney disease.
Anything affecting the 3 filtration pressures will affect the GFR (e.g. severe blood loss)
Urine formation; glomerular filtration constituents (pass into filtrate)
Blood constituents that pass into glomerular filtrate:
Water
Mineral salts (electrolytes)
Amino acids
Glucose (usually reapsorbed back into blood)
Ketoacids
Hormones
Creatinine
Wastes (urea, uric acid, toxins)
Urine formation; glomerular filtration constituents (remain in blood)
Blood constituents remaining in glomerular capillaries:
Leukocytes
Erythrocytes
Platelets
Plasma proteins
Urine formation; Colloid osmotic pressure and associated issues - albuminuria and oedema
Colloid osmotic pressure = a form of osmotic pressure exerted by proteins (notably albumin)
Damage to the glomerular capillaries can lead to plasma protein loss into urine.
Albumin leaks into the filtrate leading to albuminuria.
Less albumin in blood makes it hypotonic and fluid moves via osmosis from blood into tissues.
Blood volume decreases and interstitial fluid volume increases causing oedema.
Urine formation; Tubular reabsorption
About 99% of glomerular filtrate is reabsorbed into the bloodstream along the renal tubules & collecting ducts, including:
Water (65% in PCT)
Amino acids & glucose
Electrolytes.
Substances are reabsorbed by active & passive processes. They pass into nearby blood vessels & are returned to general circulation. Most reabsorption occurs in the Proximal convoluted tubule (PCT)
Urine formation; Tubular secretion
The blood and tubule cells also secrete certain materials into tubular fluid, inc:
Waste products (iron acid, urea, creatinine, ammonium ions)
Certain drugs (e.g. penicillin)
Excess ions such as H+ (pH regulation)
This allows these substances to be removed from the blood & excreted in urine
Urine formation; Hormones
Five hormones affect kidney reabsorption of sodium, chloride, calcium and water as well as the secretion of potassium:
1) Angiotensin II
2) Aldosterone
3) Antidiuretic hormone
4) Atrial natriuretic peptide (ANP)
5) Parathyroid hormone
Renin-Angiotensin-Aldosterone System (RAAS)
The RAAS increases blood pressure.
If systolic BP is below 100mmHg, the afferent arteriole walls are stretched less, this causes:
1) The enzyme renin to be released by the kidneys into blood
2) Angiotensinogen to be converted to angiotensin I (in liver)
3) Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme (ACE) in the lungs
4) Angiotensin II causes release of aldosterone from the adrenal cortex
Aldosterone acts on the kidneys to stimulate reabsorption of salt (NaCl) and water (H2O)
Angiotensin II also acts directly on blood vessels, stimulating vasoconstriction (narrowing)
Hormones; Angiotensin II
Triggers vasoconstriction, which increases blood pressure.
Angiotensin II also triggers the pituitary gland to release anti-diuretic hormone (ADH), and stimulates adrenal cortex to produce aldosterone.
Aldosterone increases renal sodium and water reabsorption
Hormones;
Antidiuretic hormone (ADH)
Increases Blood pressure.
Reduced water concentration in the blood and lowered blood volume causes increased blood osmotic pressure.
Osmoreceptors in the hypothalamus stimulate the posterior pituitary to secrete ADH.
ADH increases the permeability of the distal convoluted tubules, increasing water reabsorption in the kidneys, thereby aiding the rebalancing of the osmotic pressure.
Hormones; Atrial Natriuretic Peptide (ANP)
Lowers Blood pressure.
ANP inhibits reabsorption of Na+ & water in the renal tubules.
A large increase in blood volume promotes release of ANP from the heart. ANP is released from the myocardium in response to atrial stretch.
ANP also suppresses the release of ADH & aldosterone (it overrides these).
These effects increase urine output & reduce blood volume (and hence lower blood pressure)
Parathyroid Hormone (PTH)
PTH is released by the parathyroid gland in response to low blood calcium levels.
PTH increases blood calcium levels by:
1) Stimulating renal reabsorption of calcium and magnesium
2) Increasing osteoclastic activity
3) Stimulating calcitriol (Vit D) release (increases gut calcium absorption)
Kidneys; Urine flow (process from nephrons to calyces)
Urine formed in the nephrons drains into papillary ducts in the renal papillae of the renal pyramids.
The papillary ducts drain into cup-like structures called minor and major calyces.
From the major calyces, urine drains into a single large cavity called the renal pelvis and then out to the bladder through the ureters.
Calyx = cup
Micturition
The discharge of urine from the bladder.
When the volume in the bladder exceeds 200-400ml, stretch receptors in the bladder wall transmit nerve impulses to the spinal cord.
In infants, this generates a micturition reflex leading to contraction of the detrusor muscle, and relaxation of the internal & external urethral sphincters.
In adults, the nervous system has matured adequately to consciously inhibit reflex contraction of the bladder & relaxation of the internal sphincter & pelvic floor muscles.
Although urination occurs via a reflex, we learn to initiate a& stop micturition voluntarily in early childhood.
Urine composition
We produce 1-2L of urine in 24 hours.
It should be yellow/ amber coloured.
Odour-slightly aromatic, sweeter in diabetics.
pH varies from 4.5-8 (average 6).
Composition:
Water (96%)
Waste products - Urea (2%), Uric acid & Creatinine
Ammonia
Electrolytes & Ions (Na, K, Cl, P, S)
Hormones
Oxalates
Homeostasis - Systems
Integumentary: Kidneys convert Vit D precursor made in the skin into its active form calcitriol
Skeletal; Kidneys help adjust blood calcium levels, required for contraction
Muscular; Kidneys help adjust blood calcium levels, required for contraction
Nervous; Kidneys can perform gluconeogenesis to provide glucose for neurons, esp. during fasting or starvation
Endocrine; Kidneys produce calcitriol and erythropoietin
Lymphatic; Adjustment of water reabsorption affects the volume of interstitial fluid & lymph. Urine flushes out microbes.
Respiratory; The lungs & kidneys help adjust pH of body fluids
Digestive; Calcitriol increases absorption of dietary calcium
Reproductive; In males, the urethra is a passageway for semen & urine
Cardiovascular system; Kidneys can alter blood volume & pressure by adjusting water reabsorption (renin)
Medical; examination – signs and symptoms of urinary pathologies - Urinary tract pathology:
Signs & symptoms which indicate urinary tract pathology:
Frequent & painful urination with urgency
Red urine (e.g. blood)
Pain in the loin
High urine volume with great thirst
Low or no urine volume
Nausea & vomiting
Oedema
Exhaustion
Medical; examination – signs and symptoms of urinary pathologies - Renal disease:
Signs of renal disease;
Pallor (due to anaemia – not producing erythropoietin)
Frothy urine (due to proteinuria)
Oedema (protein loss)
Signs of itching of skin (uraemia)
Altered mental state (common in UTI’s)
Puffy face & bags under eyes
Dehydration & flapping tremor (too much urea)
Medical; Urinalysis – dipstick
Urinalysis can be divided into dipstick analysis and microscopy. They assess these parameters:
Dipstick:
Leukocytes
Ketones
Nitrates (bacteria)
Urobilinogen
pH
Erythrocytes
Protein
Glucose
Specific gravity (the concentration
Medical; Urinalysis – microscopy
Urine microscopy:
Volume / colour/ odour
pH
Leukocytes
Erythrocytes
Casts (clumps of molecules that have formed in nephron e.g. RBC, WBC, proteins, bacteria = show disease process)
Bacteria
Specific gravity
Microalbuminuria (diabetes)
Medical; Urinalysis – parameter & Indications
Leukocytes = Urinary tract infection (UTI)
Ketones = Keto-acidosis
(complication of diabetes mellitus) or ketone diet
Nitrates (bacteria) = UTI
Urobilinogen = Liver pathology
Erythrocytes = UTI, tumour, kidney stone
Protein = Kidney disease
Glucose = Diabetes mellitus
Specific gravity = Dehydration, glucosuria, proteinuria
Casts = Nephron disease
Microalbuminuria = Kidney disease (i.e. diabetic kidney)
Medical; Blood tests
Blood tests:
Glomerular filtation rate (GFR)
Urea, Creatinine, Electrolytes
Inflammatory markers; ESR (Erythrocyte Sedimentation Rate)
C reactive Protein (CRP) Leukocytes
Medical; Examinations
Medical examinations;
Ultrasound
Renal arteriography (X-ray to see blood vessels)
X-rays
CT (ureteric obstruction)
MRI (malignancy)
Cystoscopy (bladder camera)
Key terminology: dysuria
Dysuria = painful, burning urination (Dys – discomfort)
Medications: Diuretics
Medications which increase loss of sodium and water from the kidneys.
Diuretics reduce water & sodium reabsorption from the kidney tubules
Used for treatment of Oedema & hypertension
Three groups;
Thiazide diuretics (act on DCT)
Loop diuretics (act on loop of Henle)
Potassium sparing diuretics (act on collecting ducts)
Cause excessive excretion of potassium, sodium, chloride & magnesium
It is essential to replace lost electrolytes.
Foods such as celery act as a diuretic (foods, herbs, acupuncture – stimulate diuresis)
Renal Dialysis
Also known as ‘renal replacement therapy’.
Dialysis filters the blood & removes waste.
Used for patients in renal failure, whereby it mimics excretory function of kidneys to remove wastes/balance electrolytes, etc.
Two types: Haemodialysis & Peritoneal Dialysis
Both carry increased risk of infection, so often given antibiotics
Renal Dialysis; Hemodialysis
1) Hemodialysis:
Removing waste products (e.g. urea, creatinine) & water from blood through a machine
Usually in hospital but can be out-patient. Usually required 3 x week, 3-4 hours each session
Anticoagulants are used to prevent blood clotting
Adverse effects include hypertension (removal of too much fluid)
Renal Dialysis; Peritoneal Dialysis
Peritoneal Dialysis:
Utilises the peritoneum’s structure as a highly vascular semi permeable membrane, to allow for diffusion of fluids and dissolved substances
A tube is inserted into the abdomen which administers dialysis fluid, through which waste products diffuse into. Removal occurs via a shunt
Often administered at home. Takes longer than haemodialysis but is often more comfortable.
Excess water can be removed by changing dialysis solution
Significant risk of peritonitis at site of tube exit
Bladder capacity
Total capacity – 600-700ml, desire to urinate occurs when 200ml is exceeded.
Anatomy and function: kidney - renal pyramid and calyces
The apex of each renal pyramid is called a renal papilla (location where urine passes through into minor and major calyces)
Together, the renal pyramids & renal cortex make up the ‘functional’ portion of the kidney. Within this area are the functional units of kidney – nephrons
Urine formed by nephrons drain into the minor and major calyces
Key terminology; polyuria
Polyuria = Large quantity of urine (Poly – many)
Key terminology: oliguria
Oliguria = little urine (<400ml day)
Key terminology; Anuria
Anuria = no urine (A = absence)
Key terminology; proteinuria
Proteinuria = Protein in urine
Key terminology: bacteriuria
Bacteriuria = Bacteria in urine
Key terminology: nocturia
Nocturia = Night urination (waking to urinate) (Noct – nocturnal)
Key terminology: haematuria
Haematuria = Blood in urine
Bladder: trigone
Trigone (small triangular area on posterior floor of bladder) is bordered by two ureteral openings and the urethra opening.
Urine filtration; glomerular filtration rate (GFR) levels
Chronic kidney disease stages;
Stage 1: <90 ml/min
Stage 2: 60-89 ml/min
Stage 3: 30-59 ml/min
Stage 4: 15-29 ml/min
Stage 5: <15 ml/min
