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Urinary System. Exercises 40 and 41. Organs of the Urinary System. 2 kidneys Urinary bladder 2 ureters Urethra Primary function is to filter blood, and reabsorb water and needed substances back into blood. Remaining water and wastes are removed in urine.

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Urinary system

Urinary System

Exercises 40 and 41

Organs of the urinary system
Organs of the Urinary System

  • 2 kidneys

  • Urinary bladder

  • 2 ureters

  • Urethra

  • Primary function is to filter blood, and reabsorb water and needed substances back into blood. Remaining water and wastes are removed in urine.

Urinary system

Location of kidneys
Location of kidneys

  • Between T12 and L3

  • Partially protected by 11th and 12th ribs

  • Right kidney is lower than left

  • Kidneys and ureters are retroperitoneal

  • Protected by three layers:

    • Renal capsule

    • Adipose capsule

    • Renal fascia


  • Renal hilum – ureter, blood and lymphatic vessels

  • Renal sinus

  • Renal cortex

  • Renal medulla

    • Renal pyramids

    • Renal papilla

  • Renal columns


Functional unit of kidney

Number constant from birth

Can function on 2/3 of one kidney

Forms the urine

Duct system
Duct system

  • Minor calyces

  • Major calyces

  • Renal pelvis

  • Ureter

  • Urine is not changed after it leaves the collecting duct

Urinary system

  • Kidneys = 1% of body mass

  • Receive 15-30 % of blood flow

  • Blood supplied to kidney by renal artery

  • Afferent arteriole divides into ball shaped capillary network called the glomerulus.

  • Capillaries rejoin to form efferent arteriole, then peritubular capillaries

  • Vasa recta

Functions of the nephron
Functions of the Nephron

  • Filtration

  • Tubular reabsorption

  • Tubular secretion

Structure of a nephron
Structure of a nephron

  • Renal corpuscle

    • Glomerulus

    • Glomerular capsule or Bowman’s capsule

  • Renal tubule

    • Proximal convoluted tubule

    • Nephron loop or loop of Henle

    • Distal convoluted tubule

    • Collecting duct

Bowman s capsule
Bowman’s capsule

  • Outer layer - simple squamous epithelium

  • Inner layer – modified simple squamous epi.

    • Cells called podocytes

    • Projections are pedicels

  • Endothelium of capillary and podocytes form the endothelial-capsular (filtration) membrane.

Filtration membrane
Filtration membrane

  • Fenestrated endothelium – prevents the passage of cells

  • Basement membrane of glomerulus – prevents passage of large proteins

  • Slit membrane (between pedicels) – prevents the passage of medium sized proteins

Urinary system

Renal physiology
Renal Physiology cells and a basement membrane.

  • Glomerular filtration – most substances easily filtered

  • Filtrate = 180 L/ day but urine = 1-2 L /day

  • Filter is thin

  • Glomerular capillaries are long

  • Capillary blood pressure is high

    (afferent arteriole diameter > efferent arteriole)

Urinary system

  • Filtration fraction cells and a basement membrane. is the percentage of plasma that becomes filtrate, usually 16-20 %.

  • Glomerular Filtration Rate (GFR) is the amount of filtrate formed in both kidneys per minute; normally about 125 ml / min.

Renal autoregulation
Renal autoregulation cells and a basement membrane.

  • JGA senses Na+, Cl- and water

  • When these ↓, JGA dilates afferent arteriole, ↑ blood pressure in glomerulus

Hormonal regulation
Hormonal regulation cells and a basement membrane.

  • When BP ↓, JGA secretes renin which converts angiotensinogen to angiotensin I, angiotensin I is converted to angiotensin II in the lungs. Angiotensin II is a potent vasoconstrictor. It also stimulates the release of aldosterone, and stimulates the thirst center in the hypothalamus and release of ADH from the posterior pituitary gland.

Tubular reabsorption
Tubular reabsorption cells and a basement membrane.

  • Volume of fluid that enters the proximal convoluted tubule in ½ an hour > total plasma volume.

  • Reabsorb water, glucose, amino acids, urea and ions, esp. Na+, Cl- and K+

  • Na+ diffuses into cells, but is actively pumped out into interstitial fluid

  • Promotes reabsorption of water

Dct and collecting ducts
DCT and collecting ducts cells and a basement membrane.

  • By end of DCT 90 % of water and solutes reabsorbed.

  • Aldosterone causes principal cells to synthesize sodium pumps. Also causes potassium to be secreted into urine.

  • ADH stimulates cells to put water channels into membranes. ADH is responsible for facultative (responding to need) water reabsorption.

Tubular secretion
Tubular secretion cells and a basement membrane.

  • Two main functions:

  • Secretion of substances to eliminate them from body – ions, nitrogen-containing waste (urea, creatinine) and certain drugs

  • Secretion of H+ helps to maintain blood pH

Urinary bladder
Urinary bladder cells and a basement membrane.

  • Posterior to pubic symphysis

  • Stores urine prior to micturition

  • Trigone – between openings of ureters and internal urethral orifice – mucosa is firmly bound to muscularis.

  • Muscosa, submucosa, muscularis (detrusor muscle), and serous coat.

Evaluation of kidney function
Evaluation of kidney function cells and a basement membrane.

  • Blood Urea Nitrogen (BUN) – urea is a breakdown product of proteins

    • Influenced by diet

  • Creatinine – end product of muscle metabolism

    • Normally constant

    • Can determine creatinine clearance

Normal urine
Normal urine cells and a basement membrane.

  • Transparent yellow

  • Contains ions : Na+, Cl-, K+ ; nitrogenous wastes: ammonia, creatinine, urea and uric acid; and foreign chemicals: drugs, pesticides, food additives, etc.

  • Suspended solids in trace amounts: bacteria, blood cells, casts.

Not normally present
Not normally present cells and a basement membrane.

  • Albumin

  • Glucose, Acetone– diabetes mellitus

  • Bile – liver disease, obstruction of bile ducts, hemolytic disease

  • pH 4.6 -8.0

Specific gravity
Specific gravity cells and a basement membrane.

  • 1.001 -1.035

  • Damage to tubules , s.g. fixed at 1.010 = filtrate

  • Diabetes insipidus (lack of ADH) -

    • 1.003

  • Diabetes mellitus – “sugar diabetes”

    • 1.030 osmotic diuresis

  • Emesis or fever –

    • 1.040