3.3 Theroleofhormoneinhuman

3.3 The Role of Hormones in Humans

What is the human endocrine system?  System that control the secretion of hormone in the body.  Consists of  Endocrine glands  Hormones

Human Endocrine System

a) Endocrine glands ■ Are ductless (no duct or tube) glands. ■ Release hormones directly into the interstitial fluid and subsequently into the bloodstream

a) Endocrine glands

b) Hormones ■ Chemical messengers produced by endocrine glands  Travel in the blood,  Affect and influence only specific target cells  Bind to specific receptor molecules on the surface of the plasma membrane of the target cells

How endocrine system work

The Need for The Endocrine System  The endocrine system and the nervous system play important roles in maintaining homeostasis.  A correction mechanism in the body which reacts through hormones or nerves to correct the values of physical or chemical factors that are distorted from the normal value

The Need for The Endocrine System  The endocrine system usually

complements the nervous system.  When we dehydrated, our blood osmotic pressure increase. This stimulates neurones in the hypothalamus which in turn active cells in the pituitary gland to release the antidiuretic hormone (ADH). ADH causes the kidney to retain more water. Thus, the osmotic pressure decreases and returns to normal again

The Need for The Endocrine System 1. Involve in Physiological processes (e.g. menstrual cycle, the development of secondary sexual characteristics and growth)  The hormones released by the endocrine system regulate a wide range of activities (e.g. rate of heartbeat, metabolism, sugar level and salt concentration.

Differences between the nervous and the endocrine systems Characteristics

Nervous Nervous System System

Endocrine System

Types of message

Electrical signals (nerve impulses)

Chemical signals (hormones)

Transport

Via neurones

Via the bloodstream

Speed of transmission

Rapid

Slow

Area of response Nature of the response Duration of effect

Various destinations (to the target cells) Causes changes in the Causes muscles to contract metabolic activity Specific locations

Temporary

Long-lasting

•Growth, reproduction, Body processes •Controls both voluntary and development involved involuntary actions •Control involuntary action

Test Yourself hypothalamus

pituitary gland

thyroid gland thymus gland

adrenal gland pancreas

ovary

testis

Function of hormones

Reproduction

Growth

Homeostasis

Follicle – stimulating Growth hormone, Insulin, glucagon, hormone, Luteinising Thyroid-stimulating antidiuretic hormone hormone, Oestrogens, Hormone and and adrenaline Progesterone and thyroxine Androgens

Endocrine Gland, Function & Hormones Secreted

Endocrine Gland, Function & Hormones Secreted

Endocrine Gland, Function & Hormones Secreted

Test yourself 1. What is the human endocrine system? 2. What is hormone? 3. How many glands do a person have and what are they? 4. Give an example of hormone release by each gland.

Regulation of Hormone Secretion 1. An endocrine gland releases its hormone when stimulated. 2. Hormone secretion is regulated to prevent over production or under production.

Regulation of Hormone Secretion Hormone secretion is regulated by

Signals from the nervous system

The level of Other hormones specific substances in the body

The regulation of hormone secretion by signals from the nervous system 1. Hypothalamus • Has specialised cells called neurosecretory cells which produce hypothalamic releasing and inhibiting hormones • Link the nervous and endocrine system • Controlling the secretion of hormones from the pituitary gland to maintain homeostasis

The regulation of hormone secretion by signals from the nervous system

The regulation of hormone secretion by signals from the nervous system • • • •

The pituitary gland is the ‘master’ endocrine gland Secretes several hormones that control other endocrine glands Controlled by the hypothalamus Consists of two parts: the anterior and the posterior pituitary

The regulation of hormone secretion by signals from the nervous system • •

•

Others endocrine glands that secretions are regulated by nervous system are: The adrenal medulla – receives impulses from the efferent nerves of the nervous system and secretes adrenaline in response The pancreas – after meal, the pancreas receives efferent impulses from the CNS to secrete insulin to reduce the blood glucose level

The regul ati on of hormone secretion by other hormones •

The secretion of thyroxine is regulated by the thyroid-stimulating hormone b) The pituitary gland secretes the thyroidstimulating hormone (TSH) to stimulate the thyroid gland to produce thyroxine c) The more TSH the thyroid gland receives, the more thyroxine it secretes d) In turn, less TSH reduces the activity of the thyroid gland, causing a drop in the level of thyroxine

The regul ati on of hormone secretion by other hormones  Hormones luteinising hormone (LH) stimulates secretion of oestrogen, progesterone and testosterone.  Hormone adrenocorticotrophic hormone (ACTH) stimulates adrenal cortex to release adrenalin and noradrenaline hormones from adrenal gland

The regulation of hormone secretion by the level of specific substances in the blood •

E.g. blood glucose level increase → the pancreas produces insulin → causes an increase in the glucose uptake by cells → the cells either metabolise the glucose or convert it to glycogen • What happen if blood glucose level decrease? → Pancreas will secrete more glucagon which converts glycogen to glucose

Test yourself 1. What regulates the secretion of hormone? 2. Explain in brief how each factor regulates the secretion of hormone.

The involvement of both the nervous system and the endocrine system in a 'fight or flight" situation • During a threatening situation, for example, when a dog suddenly barks and chases you, our heart will beats faster. • During these moments of 'fight or flight', the hypothalamus sends nerve impulses directly to the adrenal medulla to secrete adrenaline and noradrenaline.

The involvement of both the nervous system and the endocrine system in a 'fight or flight" situation  The adrenal medulla, which is the innermost region of the adrenal gland, has neurones from the sympathetic division of the autonomic nervous system.  In this situation a heartbeat, breathing rates, blood pressure, blood glucose level and metabolic activity will increases.  The skeletal muscles become more energised and enable a person to fight off an attacker or flee immediately from danger.

The Sequence of Events

Hormonal Imbalances & Related Diseases

Hormonal Imbalances & Related Diseases

Hormonal Imbalances & Related Diseases

Exercise Do Checkpoint 3.3 on page 97 in your textbook. Change question No. 3 to this question: 3. How do excess hormone removed from the blood?