Biology 12

Excretory System Notes

Metabolic Wastes Produced By Body

1. Nitrogenous wastesa) Ammonia (NH3)

Toxic

b) Urea

c) Uric acid

If uric acid crystals collect in joints → it results in a

painful condition called __________

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Note: Heme is broken down in the liver to produce ___________—excreted in kidneys and makes urine yellow

d) Creatinine

Creatine is converted into Creatinine and excreted in urine

2. Water & Other Wastes

a) Water End product of metabolism as well as being consumed

by food and drink

b) Inorganic salts

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c) Carbon dioxide Product of cellular respiration

d) Bile pigments From breakdown of heme portion of haemoglobin have

________ which is further broken down into _______

Four excretory organs

a) Skin

Mostly perspire to cool down though

b) Liver

Also excretes cholesterol and excess fat-soluble vitamins

c) Lungs

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d) Kidneys Produces ______— composed of (95%) water &

nitrogenous wastes from breakdown of amino acids, nucleotides and creatinine, as well as (5%) inorganic salts

The Urinary System

A. Functions of Urinary System

Maintain H2O balance (important for blood pressure)

Maintain acid-base balance keeping the blood pH constant at around 7.4 by excreting excess H+ ions and reabsorbing HCO3- ions

B. Path of Urinea) Kidneys

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below diaphragm and dorsal aspect of abdomen produce urine

b) Ureters

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transport urine by __________ ___________ in spurts

to the urinary bladder

c) Urinary bladder

Temporary storage place for urine

d) Urethra

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Longer in males than females

Urination occurs when bladder full → stretch receptors in bladder → spinal cord → nerve signals to bladder → contract and urethral sphincters relax to allow for urination

Anatomy of the Kidneys

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a) Renal Capsule Adipose (fat) tissue covers renal capsule for trauma

protection

b) Renal Cortex Contains glomeruli (glomerulus sing.), Bowman’s capsule,

proximal and distal convoluted tubulesc) Renal Medulla

Inner part of kidney8

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Contains Loop of Henle and collecting ducts forming cone

shaped _________ _________ Where find Loop of Henle and Collecting Ducts

d) Renal Pelvis Continuous with ureter

e) Nephrons Filter blood

_____ artery → _______ arteriole → forms __________ (knot of capillaries inside glomurellus capsule)→ ________ arteriole → _____________ capillaries (surround nephron) → _________ → ________ vein→ inferior vena cava

Figure: Diagram of Nephron

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Glomerulus Receives blood from afferent arteriole Where ____________ _____________ occurs

Bowman’s Capsule

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Inner part contains _________—cells with long processes that

cling to glomerular capillaries leaving small holes that facilitate passage of fluids and other materials into Bowman’s capsule—called _____________ __________—small molecules forced from glomerulus into Bowman’s capsule

Note: Bowman’s capsule and Glomerulus are sometimes called the glomerular capsule

Proximal Convoluted Tubule Lined by cuboidal epithelium cells with _____ border (microvilli)

Brush border ↑ surface area for tubular reabsorption of filtrate Where _________ reabsorption occurs—i.e. water, glucose, a.a.

and salt returned to blood by diffusion and active transport

Reabsorbed Filtrate Nonreabsorbed FiltrateComponents Components

Most water Some waterNutrients Nitrogenous wastesRequired salts (ions) Excess SaltsLoop of Henle

Where have salt and water reabsorption

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Distal Convoluted Tubule Made of cuboidal epithelium (no brush border) Move molecules from peritubular capillaries (i.e. blood) into distal

convoluted tubule lumen to form urine—called tubular secretion

Collecting Ducts

Carry urine to renal pelvis

Urine Formation

3 processes involved

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A. Glomerular Filtration

Blood entering glomerulus divided into 2 parts:

(i) Filterable components

Include such things as water, creatinine, HCO3-, nitrogenous wastes such as urea, nutrients such as glucose, vitamins and salts such as Na+, K+, Cl-, etc.

Above filtrate called ____________ filtrate This filtration process is called _________ filtration and is

about 125 ml per minute for all nephrons in both kidneys

Note: about 180 L of water and many small molecules are filtered daily—if not returned to blood person would die of malnutrition and dehydration due to loss of these substances in urine

(ii) Non-filterable component

Stay in blood

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Molecules that escape filtration leave glomerulus by the efferent arteriole

B. Tubular Re-absorption & Secretion

____________ reabsorption is the process involving both active and passive transport of substances back into the blood (i.e. peritubular capillaries) from proximal & distal convoluted tubule as well as the loop of Henle

___________ secretion is the process whereby substances are transported into proximal and distal tubules from interstitial fluid or blood

(i) Proximal Convoluted Tubule

Passive Reabsorption: Particles move along concentration gradient

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Water re-absorption also helped along by osmosis since blood has higher solute concentration than proximal tubule

Active Re-absoprtion Nutrients and salts also actively absorbed from proximal tubule 60-70% of Na+ ions actively pumped out of proximal tubule to

peritubular capillaries Na+Cl- thus flows back into peritibular capillaries ↑ osmolarity of

blood

This happens until most of NaCl and water have been reabsorbed (i.e. back into blood)

H+ and NH3 are secreted from blood into proximal tubule

Tubular Secretion at Proximal Tubule Uric acid Many drugs H+ NH3

(ii) Descending Limb of Loop of Henle

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Epithelium not permeable to salt along descending limb but permeable to water

Results in ↑ osmolarity of filtrate as descend loop

(iii) Ascending Limb of Loop of Henle

As filtrate ascends thin segment, NaCl diffuses out into

interstitial fluid—contributes to ↑ osmolarity in interstitial fluid of medulla

Active transport of NaCl into interstitial fluid does occur in

thick segment of loop however to maintain a gradient Above relationship between ascending and descending limb of

loop of Henle is known as the countercurrent multiplier—where flows in ascending and descending limb counteract each other

H2O leaves descending limb by diffusion due to above gradient(iv) Distal Convoluted Tubule

K+, H+, NH3 , uric acid, creatinine, & penicillin are secreted into

distal tubule from blood

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HCO3- also reabsorbed to peritubular capillaries from distal

tubule→ helps to control pH of blood as needed

(v) Collecting Duct As descend the collecting duct, tonicity ↑in interstitial fluid

(recall what happens in ascending loop of Henle)

Loss of water concentrates urea in filtrate → some urea diffuses out into interstitial fluid from lower part of collecting duct→ ↑ osmolarity → helps to make concentrated urine

Note: collecting ducts joined to distal tubules of many different nephrons

Regulatory Function of Kidneys

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A. Regulation of blood volume & blood pressure

(i) ADH (Antidiuretic Hormone)

Sensed by posterior pituitary→ releases ADH

Results in ↓ in amount of urine production

Note: if adequate or too much water is drunk, ADH will be released in small amounts or not be released at all

Diuresis = increased urine production Certain drugs and caffeine are diuretics as ↓ Na+ re-absorption

and ↑ GFR

(ii) Juxtaglomerular Apparatus & Renin/Angiotensin Area of contact between _________ arteriole and ______

tubule Specialized cells of afferent arteriole sense b.p.

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As a result, juxtaglomerular cells of Juxtaglomerular apparatus secretes enzyme _____

Renin changes angiotensinogen (plasma protein made by liver) to angiotensin I

Angiotensin II is a vasoconstrictor on its own Angiotensin II also stimulates adrenal cortex to release

______________ Aldosterone causes ↑ reabsorption of Na+ ions and

therefore ↑ water reabsorption from nephron (i.e. ↑ water reabsorption from proximal tubule, distal tubule and collecting ducts of nephron)

(iii) Atrial natriuretic peptide/hormone (ANH or ANP) ANH inhibits renin release from juxtaglomerular apparatus

Thus, ANH causes ↑ secretion of Na+ leading to ↑ water excretion from osmosis in urine→ decreased blood volume and blood pressure

B. Maintenance of blood pH

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One way is to increase breathing rate to get rid of hydrogen ions

though the following reaction: H+ + HCO3- → H2CO3 → H2O + CO2…recall that this happens in the lungs and is relatively fast

If blood acidic:

↑ Reabsorption of HCO3- and Na+ back into blood

Note: NaHCO3 is a base

If blood basic:

Get ↓ reabsorption of HCO3- & Na+

Summary: the kidneys reabsorb bicarbonate ions and excrete hydrogen ions as needed to maintain a normal pH of blood.

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