role of hormones in humans

Role of Hormones in

Humans Endocrine System, Endocrine glands and

Hormones

1

Role of Endocrine System

• Endocrine system : controls the body’s activity by

releasing chemicals in the blood stream that can regulate

the activities of organs and tissues

• Endocrine system : made up of endocrine glands (does

not have ducts)

• Produce and release hormones directly into the

bloodstream

• Body’s responses to hormones are slower and longer-

lasting than the responses to nerve impulses 2

Endocrine Glands

• Major glands of the endocrine system include the

pituitary gland, thyroid gland, adrenal glands, pancreas

and gonads (testes and ovaries)

• The pituitary glands is controlled by the hypothalamus in

the brain

• It secretes several hormones that directly regulate many

body functions and control the activities of another

endocrine glands 3

Hormones

• Chemicals in the

bloodstream that can

regulate the activities

of organs and tissues

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Regulation of hormone

secretion

• An endocrine gland released its hormones more

frequently when stimulated, thus increasing their

concentration in the blood

• Hormone secretion is regulated by;

• a.) signals from the nervous system

• b.) other hormones

• c.) the level of specific substances in the body 10

Secretion of Hormones

regulated by another hormone

• Hormone thyroxine : regulated by the thyroid-stimulating

hormone

• A high level of thyroxine inhibits the release of the

thyroid stimulating hormone and stops the release of

additional thyroxine

• A low level of thyroxine? 11

Secretion of hormones

regulated by levels of certain

substances

• Substances in the blood such as the level of glucose can

control the secretion of hormones.

• A high level of glucose stimulates the pancreas to secrete

insulin

• The excess glucose is then converted to glycogen and this

decreases the level of glucose in the blood

• When the level of glucose gets too low?

13

Secretion of hormones

regulated by nervous system

• Some endocrine glands are controlled by the nervous

system

• The hypothalamus receives nerve impulses from the

receptors which then stimulate the pituitary gland to

release hormones

• The adrenal gland is also stimulated to release hormones

by the nervous system

15

Neurosecretory cells in the

hypothalamus

ADH and Oxytoxin

These hormones pass through the axons into the posterior pituitary cells (stored in the

synaptic terminals)

ADH and Oxytoxin are secreted from the synaptic

terminals into the bloodstream

Hypothalamus RH and IH

These hormones are carried in the bloodstream

to the anterior pituitary

RH : stimulate the secretion of the anterior pituitary hormone

IH : suppress the secretion of anterior pituitary hormone 18

Coordination Involving Both

Nervous System and Endocrine

System (Fight or Flight situation)

• During a threatening situation, for example when fierce

dog suddenly barks at you, the hypothalamus sends nerve

impulses directly to the adrenal medulla

• The adrenal medulla, the innermost region of the adrenal

gland has neurones from the sympathetic division of the

ANS

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Sequence of events that take place

during fight or flight situations

• 1. Nerve impulses from the hypothalamus

• 2. Stimulate the neurones from the sympathetic division

• 3. Stimulate the cells of the adrenal medulla to secrete adrenaline and noradrenaline

• 4. Adrenaline and noradrenaline cause…..

• 5. The heartbeat and breathing rates, blood pressure, blood glucose level and metabolic activity to increase

22

• When a person is in a stressful situation, the nervous and

endocrine systems both work together to bring about

immediate responses to cope with the situation

• Once these mechanisms successfully counteract the

danger, the bodily changes that occurred return to normal

23

Effects of Hormonal

Imbalance

• Improper functioning of an endocrine gland may result in

a disease or a disorder

• Goitre : enlargement of the thyroid gland due to iodine

deficiency. Too little thyroxine is produced which causes

the thyroid gland to enlarge to compensate for this

deficiency

• Cretinism : lack of thyroxine in children; results in

mental retardation and dwarfism. In adults, a condition

called hypothyroidism / myxedema 24

• Hypothyroidism : characterised by an enlarged thyroid gland, slow heart rate, fatigue and weight gain

• Hyperthyroidism : too much of thyroxine; enlarged thyroid gland, nervousness, rapid heart beat, bulging eyes, hand tremor and weight loss

• Gigantism : too much of growth hormones are produced during childhood, body grow quickly/ abnormally tall. Acromegaly?

• Dwarfism : too little of growth hormones is produced during childhood; the organs often fail to grow and the size of body is like that a child

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• Diabetes insipidus : lack of the antidiuretic hormone;

large volume of urine is excreted and body loses a lot of

water

• Oedema : too much of antidiuretic hormone; due to

accumulation of excess fluids in the body

• Diabetes mellitus : imbalance of insulin; amounts of

glucose in the blood may rise so high that the kidneys

excrete glucose in the urine

26

Exercise

• Question 5, SPM 2008

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Homeostasis in Humans

• Homeostasis : The regulation of the physical and chemical factors in the internal environment to maintain a constant internal environment.

• Involves monitoring changes in the external and internal environments by means of receptors and adjusting the change through a negative feedback mechanism

• Physical factors : body temperature, blood pressure

• Chemical factors : partial pressure of oxygen, carbon dioxide, osmotic pressure and sugar levels

28

The Excretory system

• Plays an important role in homeostasis

• Primary organs of the excretory system are the kidneys

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Kidneys • Help to regulate the water and salt balance in the body by

excreting more or less salt, and increasing the intake or

loss of water

• Regulate the osmotic pressure and ionic levels in the

blood

• Excrete waste products

• Regulate the blood pH 30

Human Excretory System

31

Waste products

• From metabolic reactions in the body, example : urea,

creatinine (break down of amino acids), uric acid (break

down of nucleic acids)

• Foreign substances in the diet : drugs or toxins.

32

Kidneys

• Filter blood and form urine which exits the body through

the ureters, urinary bladder and urethra

• Urine: consists of water, urea and other dissolved wastes,

and some excess nutrients.

• Has two distinct regions : a) outer light-red region (renal

cortex)

b) inner dark red region (renal medulla)

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• The renal artery supplies oxygenated blood and nutrients

to the kidney

• The renal vein carries away filtered blood to the body

35

The nephron

• The functional unit of a kidney is the nephron

• Each human kidney consists of about one million

nephrons

• A nephron consists of three major parts:

• a) the glomerulus and its associated blood vessels

• b) the Bowman’s capsule

• c) a long narrow tube called the renal tubule 36

The nephron

• The renal tubule is made up of the ;

• a) proximal convoluted tubule

• b) loop of Henle

• c) distal convoluted tubule

• The distal convoluted tubules of several nephrons join to a common collecting duct

• The Bowman’s capsule and both convoluted tubules lie within the renal cortex, whereas the loop of Henle extends into the renal medulla

• http://www.dnatube.com/video/2754/Nephron-Function 37

Bowman’s capsule

39

The nephron

• Within the kidney, each nephron is supplied with blood

by an afferent arteriole which is a branch of the renal

artery

• Each afferent arteriole divides further into a tangled

capillary network called the glomerulus

• The capillaries of the glomerulus reunite to form an

efferent arteriole 40

The nephron

• Each efferent arteriole divides to form a network of blood

capillaries surrounding the kidney tubules

• These blood capillaries are called peritubular capillaries

or the capillary network which eventually join together

into the renal vein

41

The formation of Urine

• The formation of urine involves three processes namely

ultrafiltration, reabsorption and secretion.

• Ultrafiltration occurs at glomerulus

• The high hydrostatic pressure in the glomerulus causes

many constituents of the blood to be filtered out from the

glomerulus into the Bowman’s capsule

42

Ultrafiltration

43

Ultrafiltration

• The glomerular filtrate has the same composition as the

plasma except that it does not contain any of the larger

components such as RBC and plasma proteins

• The glomerular filtrate contains water, glucose, amino

acids, urea, mineral salts and other small molecules

44

Reabsorption

• As the filtrate passes along the length of the nephron,

reabsorption occurs

• Reabsorption occurs at the proximal convulated tubule

(PCT), loop of Henle, distal convulated tubule and

collecting duct

45

Reabsorption

• At PCT, about 65% of the water in the filtrate is

reabsorbed back into the surrounding blood capillaries by

osmosis

• All the glucose, amino acids, vitamins and some salts

are reabsorbed by active transport

• Water, salts and urea passes along the loop of Henle,

about 20% of water and some salts are reabsorbed into

the capillaries 46

Reabsorption

• At the DCT and collecting duct, the amount of water and

salts that are reabsorbed into the blood capillaries

depends on the content of water and salt in the blood

• The absorption of water and salt regulated by the

endocrine system.

47

Secretion

• Secretion occurs at the DCT

• Along the tubule, waste products such as urea, uric acid

and ammonia are pumped out of the blood capillaries into

the DCT by active transport

• Some drugs and other toxic substances are also secreted

out of the blood capillaries by simple diffusion

48

Secretion

• The final glomerular filtrate which remain in the

collecting duct is called urine

• The major constituents of urine are approximately 96%

water, 2.5% nitrogenous products such as urea, uric acid,

ammonia and creatinine, 1.5% salts and other trace

elements such as bile pigments

49

Secretion

• Secretion helps to ;

• a) eliminate and increase the rate of waste removal from

the body

• b) regulate the levels of certain ions in the blood.

( Kidneys can regulate the chemical composition of the

blood – by adjusting the amount of ions to absorb or to

secrete)

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The formation of urine

51

The formation of urine

52

Osmoregulation

• The kidneys also function as an organ of osmoregulation

by regulating the salts and water balance in the body; to

maintain the blood pressure

• The water and salt content in the blood determines the

osmotic pressure in the blood

• The osmotic pressure is high when is an excess of salts

and less water in the blood 53

Osmoregulation • Osmoregulation : The process of maintaining the water

content of the blood at the constant level

• Osmoregulation : achieved mainly by regulating the

volume of urine production and excretion from the

kidneys

• This process is achieved by a negative feedback

mechanism 54

Mechanism of Osmoregulation

• Controlled by two hormones that are the ADH and

Aldosterone

• Work through a negative feedback mechanism to regulate

water and salt content in the blood by the process

Reabsorption

• The reabsorption of both water and salts determine the

final concentration and volume of urine

57

Mechanism of Osmoregulation

• When very salty food is eaten/ too much water is lost by

sweating = Osmotic pressure in the blood increases

• Osmoreceptor (sensory cells) detect the change in

osmotic pressure and trigger the pituitary gland to secrete

the ADH

• ADH increases the permeability of the walls of DCT and

collecting duct towards the reabsorption of water

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• As a result, more water is reabsorbed back from the

tubule into the blood capillaries

• This lowers the osmotic pressure to its normal level. It

also decreases the volume of urine produced. Hence the

urine produced is little but concentrated

60

Consequences of Impaired

Kidney Function

• Kidneys fail to function? – cannot carry out their function

as an excretory organ and as organ of osmoregulation

• Metabolic wastes such as urea, excess water and salts

cannot be excreted out and osmotic pressure in the blood

cannot be regulated

• How can patients with impaired kidney function be

treated? 61

Haemodialysis

• Process whereby a dialysis machine is used to remove

metabolic wastes such as excess water, urea and excess

mineral salts from the blood

62

Haemodialysis • The machine has a coiled tubing with a semi-permeable

wall bathed in a sterile dialysis fluid.

• The concentration of dialysis fluid in the machine is

maintained at a concentration similar to the blood

plasma

• The dialysis fluid is constantly flowing and changed

regularly to remove the waste substances and to maintain

the diffusion gradient between the patients’ blood and

dialysis fluid

63

Haemodialysis

• The blood from the radial artery in the patients’ arm

passes into the machine and then flows out into a vein in

the same arm

• Blood flows through the coiled tubing, the urea and salts

which are higher in concentration in the blood diffuses

across the tubing walls into the dialysis fluid which has

a lower concentration of urea and salts

65

Regulation of Blood Sugar

level

• The normal blood glucose concentration in humans is

about 90mg of glucose in 100 cm³/ (75-110mg/100ml)

• The high concentration of glucose stimulates the ß-cells

of the Islets of Langerhans in the pancreas to secrete

insulin into the bloodstream

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level

• If the glucose level falls below the normal level, ᾳ-cells

of the Islets of Langerhans are stimulated to secrete

glucagon

• Both these hormones work in opposition to each other to

regulate the blood glucose level

• Defects in the production , release and reception of

insulin by target cells can lead to diabetes mellitus 67


level

• As the PCT of the kidney cannot reabsorb all the glucose

from the kidney filtrate, glucose is excreted in the urine

• Diabetes can be controlled by insulin injections, tablets

that lower the blood glucose levels and careful diets

68

Regulation of Body

Temperature

• The skin plays an important role in regulating the body

temperature; regulating heat gain and heat loss = maintains a

constant temperature

• Thermoreceptors (cold and warm receptors) in the skin detect

changes in the environmental temperature. Hypothalamus

(temperature regulatory centre) detect changes in the temperature

of the blood flowing pass it

71

Regulation of Body Temperature

• The hypothalamus acts as the temperature regulatory

centre.

• It causes the effectors to respond by negative feedback

through corrective mechanism to restore the temperature

back to its normal level

• The effectors respond by physical means (involving the

skin) and by the process of metabolism (which involves

the endocrine glands) 74

Practising a Healthy Lifestyle

• Drugs can alter brain functions and the rates at which

neurones release neurotransmitters

• The abuse of drugs normally results in a tolerance of the

drug. This means that more and more of the drugs is

needed to produce the same initial effect on the person

• A person who is addicted to drugs will experience

withdrawal symptoms such as shivering, sweating and

nausea when he is deprived on the drug 77

• Types of drugs and their effects on the body

78

Plant Hormones

• In plants, response is controlled by chemicals called plant

hormones or plant growth regulators

• A plant hormone : a chemical substance which is

produced by the plant and influences the growth and

development of the plant

• It brings about its effect near the site of its formation or it

may be transported to other parts of the plant where it

acts 79

Plant Hormones

• Plants hormones : Auxins and Ethylene

• Plants respond to stimuli by growing in a certain

direction. This growth response is called tropism –

Auxins

• Auxins are produced in the apical meristems of the

shoots.

• Auxins promote the elongation of cells in the shoot

80

Role of Auxins in Tropism

• Auxins control the growth movements of shoots and roots

in plants

• This type of response where the direction of growth

movement is determined by the direction of the stimulus

is called tropism

• Phototropism (Direction of light from one side) : Shoots

bend towards light (+ve)

• : Roots grow away from light (-ve)

86

• Geotropism : Shoots grow upwards against the force of

gravity (negative geotropism)

• : Roots grow downwards in the direction of gravity

(Positive geotropism)

87

Phototropism

• From the experiments, we can conclude that,

• a) the tip of the coleoptile is the light-sensitive region

• b) the meristem cells at the tip of the shoot produces

auxins

• c) auxins move away from the light and accumulate in the

shaded side

• d) high concentration of auxins in shoots promote

elongation of cells in shoots

• e) auxins can diffuse through the agar block (liquid base)

but not through metals and solids 90

Geotropism • Gravity causes the tip of growing shoots and roots to

produce auxins

• Auxins diffuse into zone of elongation

• Owing to gravity, auxins move to lower side of shoot and

root

• The lower side of shoot and root has a higher

concentration of auxins that the upper side 91

Geotropism

• A high concentration of auxins in the shoot promotes

elongation of cells. Hence the lower side of the shoot

with a higher concentration of auxins will grow faster that

the upper side. (negative geotropism)

• A high concentration of auxins inhibits the elongation of

cells in the root. The upper side of the root grows faster

that the lower side. (positive geotropism)

92

Ethylene

• Synthesised during the ripening of fruits

• Occurs in fruits, leaves and stems

• Function/role : speed up the ripening of fruits by

stimulating the production of cellulase.

• Cellulase hydrolyses the cellulose in plant cell walls,

making the fruit soft 94

Ethylene

• Function/Role : promotes the breakdown of complex

carbohydrates into simple sugar. That is why a ripe fruit

tastes sweeter that an unripe fruit

95

Topical Test

• a) What is ultrafiltration? (1 mark)

• b) Explain where and how it occurs.(3 marks)

• c) What are the substances being filtered out? (3 marks)

• d) Describe how the components of the filtrate are

reabsorbed along the tubule of the nephron. (3 marks)

• e) What are the components of the filtrate that are

reabsorbed back into the capillaries? (2 marks)

• f) Describe how secretion occurs. (3 marks)

97

role of hormones in humans

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