Excretory System Yummmmmm… Nephrons

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Functions on the Urinary System

Excretion of Metabolic Wastes

Maintenance of water – salt balance

Maintenance of acid – base balance

Secretion of hormones

Excretion of Metabolic Wastes

Excrete nitrogenous wastes

Urea is the primary nitrogenous waste By product of nucleic acid breakdown Liver releases ammonia (extremely toxic to

cells) Forms with carbon dioxide to form urea

If too much uric acid is present in the blood, can precipitate causing crystal = gout

Others wastes include methane

Maintenance of Water-Salt Balance

Blood volume is closely associated with the salt balance of the body

The greater amount of salt in the blood, the greater the blood volume, the greater the blood pressure

Kidneys are responsible for filtering the blood of appropriate ions (Sodium, Potassium, Chloride etc…)

Maintenance of Acid-Base Balance

Kidneys monitor and maintain a pH of 7.4

Excretes hydrogen ions

Reabsorbs bicarbonate ions

Secretion of Hormones

Assist in the endocrine function of the human body

Releases rennin which stimulates the release of aldosterone from the adrenal glands Promotes the reabsorption of Na+ ions from the

kidney

Organs of the Urinary System

Consists of the kidneys, ureters, urinary bladder and urethra

Numbered off into groups 1-4, learn the specific function of the specific organ

Group 1: KidneyGroup 2: UreterGroup 3: Urinary BladderGroup 4: Urethra

1 person is nominated to write brief description onto the board

THE URINARY SYSTEM

Wastes filtered from blood by kidneys.

Wastes travel to bladder through ureters.

Kidney cross section:

Cortex: outer layer.

Medulla: inner layer.

Renal pelvis: hollow, central chamber.

Gross Anatomy of the Kidney

Renal Cortex: outer granulated layer that dips down

Renal Medulla: Consists of cone shaped tissues

Renal Pelvis: Is a central space or cavity that is continuous with the ureters

NEPHRONS

Multiple small tubes.

Functional unit of kidneys.

Afferent arterioles supply blood.

Branch into capillary bed or glomerulus.

Blood leaves glomerulus through efferent arterioles.

NEPHRONS CONTINUED

Glomerulus surrounded by Bowman’s capsule.

Urine carried through proximal tubule (lined with microvili) to the loop of Henle (lined with simple squamous epithelium)

Urine continues to distal tubule (cuboidal epithelial cells) and into collecting ducts.

Collecting ducts merge in renal pelvis and expel urine into ureters.

ANATOMY

Glomerular Filtration Rate

Occurs when the blood enters the afferent arteriole and the glomerulus

Due to glomerular blood pressure, water and other small molecules move from blood into the filtrated urine

Glomerular Filtration

Nephrons in kidney filter 180 liters of water per day ,including a small amount of molecules such as glucose and ions

Substance Amounted Filtered

Amount Excreted

Reabsorstion %

Water 180 L 1.8 L 99.0

Sodium 630g 3.2g 99.5

Glucose 180g 0.0 100

Urea 54g 30 44

FILTRATION

Individual nephrons have own blood supply.

Blood moves through afferent arteriole into glomerulus.

Glomerulus under high pressure.

Solutes diffuse across glomerulus walls into Bowman’s capsule.

Materials move from high pressure to low pressure.

THE FILTRATE

Not all blood components pass through capillary wall.

Small molecules and ions pass through easily.

E.g. Water, glucose, salts, amino acids.

Large molecules and structures remain in blood.

E.g. RBCs, platelets, proteins.

REABSORPTION

Urine formation water intensive.

Water and other important salts and molecules must be reabsorbed.

Active and passive transport used.

Na+ transported across nephron cell membrane.

Excess salts excreted in urine when threshold level reached.

REABSORPTION

Glucose and amino acids actively transported back into blood.

Some urea and uric acid is reabsorbed by this process.

SECRETION

Movement of wastes into nephron.

E.g. Nitrogenous wastes, surplus ions.

Active transport.

Mitochondria line distal tubule.

WATER BALANCE

Increased water intake → increased urine production.

Increased exercise, decreased water intake → reduced urine production and concentrated urine.

ANTIDIURETIC HORMONE (ADH)

Increases water reabsorption.

More concentrated urine results.

Produced by nerve cells of hypothalamus and stored in pituitary gland.

Pituitary gland releases ADH into blood.

Osmoreceptors in hypothalamus detect changes in body osmotic pressure.

Hypothalamus shrinks and sends nervous signals to pituitary gland.

ADH released into blood.

Thirst.

ADH ACTION ON NEPHRON

All parts of nephron not always permeable to water.

ADH makes upper section of distal tubule and collecting duct permeable to water.

High concentration of NaCl in interstitial fluid draws water back into interstitial space.

ANTIDIURETIC HORMONE (ADH)

ABSENT PRESENT

REGULATION OF BLOOD PRESSURE

Kidneys regulate blood pressure by controlling blood volume.

Aldosterone produced in adrenal glands increases causing water reabsorption and increased blood volume.

RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM

Blood pressure receptors near glomerulus detect drop in blood pressure.

Renin released.

Converts angiotensinogen to angiotensin.

Blood vessels constrict.

Also stimulates release of more aldosterone.