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Anouk Biology Decks > 5.1.2 - Excretion as an example of homeostatic control > Flashcards

5.1.2 - Excretion as an example of homeostatic control Flashcards

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1
Q

Give the definition of excretion.

A

The removal of metabolic waste from body.

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2
Q

What is metabolic waste?

A

The unwanted products of cell metabolism.

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3
Q

Why is excretion so important?

A

The waste products could:

  • build up & become toxic
  • act as inhibitors & reduce activity of enzymes.
  • could interfere with cell process by altering the pH.

Excretion maintains:
> normal metabolism
> homeostasis = keeps levels of some substances in blood constant.

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4
Q

What are the main excretory products?

A
  • CD. from resp.
  • nitrogen-containing compounds, e.g. urea (i.e. nitrogenous waste)
  • other compounds, e.g. the bile pigments found in faeces.
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5
Q

What are the 4 excretory organs?

A
  • lungs
  • liver
  • kidneys
  • skin
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6
Q

Outline the role of the lungs in excretion.

A
  • every cell in body produces CD. from resp.
  • CD. is passed from cells of respiring tissues into bloodstream
  • it is transported (mostly in the form of hydrogencarbonate ions) to lungs.
  • in lungs: CD. diffuses into alveoli to be excreted as you exhale.
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7
Q

Outline the roles of the liver in excretion.

A
  • has many metabolic roles
  • some substances produced will be passed into bile for excretion with faeces, e.g. pigment bilirubin.
  • liver converts excess amino acids to urea.

> amino acids: broken down by DEAMINATION. Nitrogen-containing part of molecule is then combined w CD. to make urea.

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8
Q

Outline to roles of the kidneys in excretion.

A
  • urea: passed into bloodstream to be transported to kidneys
  • urea is transported in solution - dissolved in the plasma
  • in kidneys: urea is removed from b. to come a part of the urine.
    > urine is stored in bladder before being excreted from body via urethra.
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9
Q

Outline the role of the skin in excretion.
(substances sweat contains)
(name 3 of these that are excretory products)
(why is the loss of water & salts via skin important?)

A 
Sweat contains many substances inc.: 
> salts
> urea
> water
> uric acid
> ammonia

Urea, uric acid & ammonia are all excretory products.

Loss of water & salts: important part of homeostasis - maintaining the body temp. & Ψ of b.

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10
Q

Give two metabolic products that are toxic and how they interfere with cell processes in the body.

A
  • CD. & ammonia.

- interfere by altering the pH, so that normal metabolism is prevented.

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11
Q

In what form is CD. transported in the blood?

A

As hydrogencarbonate ions.

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12
Q

Forming hydrogencarbonate ions also forms…

A

hydrogen ions.

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13
Q

Give the equation of carbonic acid formation.

Give the equation of carbonic acid dissociation.

A

CO2 + H2O > H2CO3

H2CO3 > (H+) + (HCO3-)

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14
Q

Where does carbonic acid dissociation occur?

A
  • inside the RBC., under the influence of the enzyme carbonic anhydrase.
  • can also occur in the b. plasma.
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15
Q

Give two things that H+ ions affect.

A
  • H+ ions affect pH of cyt. in RBC.

- H+ ions interact w bonds within haem.,changing its 3D shape.

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16
Q

How does the change in haemoglobin’s 3D shape affect its function?

A
  • reduces the affinity for O., affecting O., transport.

- the H+ ions can then combine w haem. forming haemoglobinic acid.

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17
Q

What happens to the CD. that is not converted to hydrogencarbonate ions?

A

It can combine directly w haem. producing carbaminohaemoglobin.

18
Q

Can haemoglobinic acid and carbaminohaemoglobin combine with oxygen as normal?

A

NO. They are unable to combine with O as normal. This reduces O transport further.

19
Q

How do H+ ions affects things in the blood plasma?

A
  • excess H+ ions can reduced the pH of the plasma.
  • maintain b.plasma pH is ESSENTIAL = changes could alter the structure of many proteins in the blood that help to transport different substances around body.
  • proteins in b. act as buffers to resist change in pH.
20
Q

If the change in blood pH is small, what happens?

A
  • the extra H+ ions are detected by respiratory centre in the MEDULLA OBLONGATA of brain.

> this causes an increase in breathing rate to help remove excess carbon dioxide.

21
Q

If the change in blood pH is big, what happens?

A
  • if b. drops below 7.35 = may cause:

> headaches, drowsiness, restlessness, tremor & confusion. Rapid heart rate & change in blood pressure = RESPIRATORY ACIDOSIS.

  • can be caused by diseases: emphysema, chronic bronchitis, asthma, or sever pneumonia.
  • blockage of airway due to swelling, foreign object, vomit = can also induce.
22
Q

How does the body deal with excess amino acids?

A
  • bod. cannot store excess AA. contain almost as much energy as carbs. Wasteful to excrete them.
  • AA. are transported to liver & potentially toxic amino group is removed (DEAMINATION).
  • amino group initially forms v soluble & toxic ammonia.
    > converted to urea. (Can be transported to kidneys for excretion.)
  • remaining keto acid can be used directly in respiration to release energy or may be converted to carb or fat for storage.
23
Q

Give the equation for the formation of keto acid and ammonia. (Deanimation)

Then give the equation for the formation of urea.

A

Deanimation: amino acid + oxygen > keto acid & ammonia.

Formation of urea: ammonia + carbon dioxide > urea + water.

symbol: 2NH3 + CO2 > (NH2)2CO + H2O.

24
Q

What is another word for liver cells?

A

Hepatocytes.

25
Q

Why does the liver need a good supply of blood and an internal structure that ensures as much blood as possible flows past as many liver cells as possible?

A

Because the liver has an important role in homeostasis.

good b. supply & internal structure =
enables liver cells to remove excess or unwanted substances from b. & return substances to b. to ensure concs. are maintained.

26
Q

The liver is supplied with blood from which two sources?

A

The HEPATIC ARTERY & HEPATIC PORTAL VEIN.

27
Q

Give the function of the hepatic artery.

A
  • oxygenated b. from heart travels from aorta via the HA. into liver.
  • this supplies the O that is essential for aerobic resp.
  • liver cells v active & carry out many metabolic processes. Many of these need energy, in form of ATP, so liver needs good supply of O for aerobic resp.
28
Q

Give the function of the hepatic portal vein.

A
  • deoxygenated b. from digestive system enters liver via HPV.
    > b. is rich in products of digestion.
  • concs. of various substances will be uncontrolled = just entered bod. from products of digestion in intestines.
  • b. may contain toxic compounds that have been absorbed from intestine.
    > important that these substances do not continue to go round bod before their concs. have been altered!
29
Q

What is the role of the hepatic vein?

A
  • b. leaves liver via HEPATIC VEIN

- HV. rejoins vena cava and b. returns to bods. normal circulation.

30
Q

What is the fourth vessel connected to the liver and what is its role?

A
  • the BILE DUCT.
  • bile is a secretion from liver which has functions in digestion & excretion.
  • BD. carries bile from liver >GALL BLADDER, = stored until needed to help digestion of fats in small intestine.
  • bile also contains some excretory products e.g. bile pigments > bilirubin = will leave bod w. faeces.
31
Q

Why do the cells, blood vessels and chambers in the liver need to be arranged in a certain way?

A

to ensure the greatest possible contact between the b. and the liver cells.

32
Q

What are lobes and what are lobules in the liver?

Give the shape of these lobules.

A
  • liver is divided into LOBES which are further divided into lobules.
  • the LOBULES are cylindrical.
33
Q

Describe in detail how the blood ends up being in close contact with the liver cells. (hint: hepatic artery, hepatic portal vein, inter-lobular vessels, sinusoid)

A
  • as HA. and HPV. enter liver, they split into smaller and smaller vessels
    > these vessels run between and parallel to the lobules: INTER-LOBULAR VESSELS.
  • at intervals, branches from HA. and HPV. enter the lobules.
    > b. from the two blood vessels is mixed & passes along chamber: SINUSOID = lined with liver cells.

> as b. flows along SINUSOID it is in close contact with the liver cells.

  • the liver cells: able to remove substances from b. & return other substances to b.
34
Q

What are Kupffer cells and what is their primary function?

Give an example of one of the products of haemoglobin breakdown.

A

Kupffer cells move about within the sinusoids.
PRIMARY FUNCTION: to breakdown and recycle old b. cells.

> one of the products of haem. breakdown is BILIRUBIN: one of the bile pigments excreted as part of the bile.

35
Q

What happens to bile made in the liver cells?

A

1) bile is made in liver cells & released into the BILE CANICULI.
2) the BC. join together to form the BD., which transports bile to GB.

36
Q

What happens when the blood reaches the end of the sinusoid?

A

1) b. reaches end of sinusoid
- the concs. of many of its components have been modified and regulated

2) at centre of each lobule is a branch of the HV. known as the INTRA-LOBULAR VESSEL.
> sinusoids empty into this vessel.

3) branches of the HV., from different lobules, join together to form HV., which drains b. from liver.

37
Q

Why are portal vessels unusual?

A
  • they have capillaries at each end

- there are also portal vessels in part of the brain to facilitate hormonal communication.

38
Q

Why do liver cells (hepatocytes) appear to be relatively unspecialised?

A
  • they have a simple cuboidal shape

- have many microvilli on their surface.

39
Q

The liver cells’ many metabolic functions include..

How is the cytoplasm adapted to these functions?

A
  • protein synthesis
  • transformation & storage of carbs
  • synthesis of cholesterol & bile salts
  • detoxification
    MANY OTHER PROCESSES.

this means the CYTOPLASM:

  • must be v dense
  • is specialised in the nos. of certain organelles that it contains.
40
Q

Give the many functions of the liver.

A
  • control of b. glucose levels, amino acid levels, lipid levels
  • synthesis of bile, plasma proteins, cholesterol
  • synthesis of red b. cells in the fetus
  • storage of vitamins A, D & B12, iron, glycogen
  • detoxification of alcohol, drugs
  • breakdown of hormones
  • destruction of red b. cells.
41
Q

Describe how the liver stores glycogen.

A
  • liver stores sugars in the form of glycogen
  • able to store approx. 100-120g of glycogen
  • the glycogen forms granules in the cytoplasm of the hepatocytes.
  • the glycogen can be broken down to release glucose into b. as required (e.g. when blood glucose levels drop)

Anouk Biology Decks (24 decks)

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