CHAPTER 15Hormones

In this chapter, you need to learn

•define a hormone as a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver.

•explain what is meant by an endocrine gland, with reference to the islets of Langerhans in the pancreas.

Lesson recap :

• Animal possess 2 coordinated systems to response to external stimuli and internal changes.

Nervous SystemNervous System Endocrine (Hormone) System

Endocrine (Hormone) System

2 Types of Glands

(a) Exocrine glands(b) Endocrine glands.

• Both glands secrete chemical substances. However the secretions of exocrine glands are carried away in a duct.

(e.g sweat glands, salivary glands)

• Endocrine glands have no ducts. The secretions are released directly into the bloodstream & carried throughout the body.

15.1

Types of glands

• Ductless glands that transport their secretions via the bloodstream

• Examples: adrenal glands, pituitary gland, and pancreas

• Ducts present to transport secretions to target organs

• Examples: sweat glands, salivary glands and pancreas

Endocrine glands Exocrine glands

Two Types of glands

Glands and the hormones they secrete

Thyroid glandSecretes thyroxine. Thyroxine controls the rate of metabolism and influences physical development.

Adrenal gland (medulla)Secretes adrenaline. Adrenaline has wide-ranging effects that prepare the body for ‘fight or flight’ situations.

PancreasIslets of Langerhans in the pancreas secrete insulin and glucagon that regulate the blood glucose concentration.

kidney

HypothalamusAn endocrine gland that regulates the secretion of some pituitary hormones.

Ovaries (in females) Secretes oestrogen and progesterone.

Testes (in males) Secretes testosterone.

Pituitary gland Plays an important role as a ‘controller’. It secretes a number of hormones, which control the functions of several other endocrine glands. This is why the pituitary gland is often referred to as the ‘master gland’.

What is a hormone?

• A hormone is a chemical substance that is produced in minute quantities by an endocrine gland.

• It is carried by the blood and it changes the activity of one or more specific target organs.

• A hormone is then destroyed by the liver.

15.1

Hormone Insulin & Glucagon

• Insulin and glucagon are hormones that regulate the concentration of glucose in the blood.

• Both are produced by the islets of Langerhans in the pancreas.

• Insulin is released when blood glucose conc. is high. • It causes the liver to convert excess glucose to

glycogen, hence reducing the blood glucose concentration.

• Glucagon is released when blood glucose conc. is low. It causes the liver to breakdown glycogen to glucose hence increasing the blood glucose conc.

15.2

Effects:

INSULIN

GLUCAGON

Effect:

15.2

Diabetes Mellitus

• There are two types of diabetes : Type 1 & Type 2

15.3

Diabetes Mellitus

• In both cases, body is unable to control blood glucose concentration .

• As a result, blood glucose becomes too high for kidney to completely reabsorb all the glucose.

• Glucose is not absorbed but excreted in urine.

• Diabetics are at risk developing infections at face and feet, may affect eyes leading to blindness.

15.3

Diabetes Mellitus

Sign of diabetic patients:• High concentration of glucose in

blood and urine.• Body become weak because no

reserve of glycogen. • Persistently high blood glucose level• Healing of wounds is slow or

difficult

15.3

Treatment

• Diet• Exercise• Insulin injection

15.3

Effects of insulin secretedAmount of insulin secreted

Effects on the body

Normal Decreases blood glucose concentration by :

(a)Increasing the permeability of cell membranes to glucose, thereby increasing rate of glucose uptake by cells.

(b)Stimulating the liver and muscle cells to convert excess glucose into glycogen for storage.

(c)Increasing oxidation of glucose during tissue respiration.

Effects of insulin secretedAmount of insulin secreted

Effects on the body

Lack of secretion

Glucose cannot be stored or utilized by cells, so blood glucose concentration rises. Some glucose is subsequently lost in the urine. This leads to a disease known as ‘diabetes mellitus’.

Since muscle cells have no reserve of glycogen, the body grows weak and continuously loses weight.

The body oxidizes fats increase of glucose to release energy.

Effects of insulin secretedAmount of insulin secreted

Effects on the body

Over-secretion of insulin

• Abnormal decrease in blood glucose concentration.

• Low blood glucose concentration results in a condition known as ‘shock’.

• Coma and death may follow.

A diabetic mum gave birth to the heaviest baby (8.7

kg) in world record in Indonesia.

According to the doctor,the baby's extreme weight was the result of

excessive glucose from his mother during pregnancy.

 1. What is an effect of insulin?

A   decreased cell respirationB   decreased absorption of glucose by cellsC   increased absorption of glucoseD   increased synthesis of glycogen

 

                  

Answer :   D

2. The graphs show the concentrations of glucose and insulin in the blood of a healthy person. Which graph shows the changes expected after a meal containing starch? 

 

                  

Answer :  A 

3. What of the effects below is not due to  insulin secretion on the body?

A.  Conversion of glucose to glycogen for storage.

B.Oxidation of glucose during tissue respiration       increases.

C.  Oxidation of fats to produce energy.

D.  Permeability of cell membranes to glucose increases.

 

                  

Answer : C

Nervous System

Nervous System

Endocrine System

Endocrine System

Comparing Hormonal & Nervous System

• Both required stimulus and serve as means of coordination and response.

• What are the differences between how they work in the aspects of:

a. Form of messagesb. Response timec. Effectors

15.5

Hormone System Nervous System

Involves chemical substances (hormones)

Involves electrical signals (nerve impulses)

Hormones carried by blood

Impulses carried by neurones

Usually slow responses Fast responses

Responses can be short-lived or long-lived

Responses are short-lived

Involuntary May be voluntary or involuntary

Can affect more than one organ.

Effects are usually localised

Differences15.5