Endocrine System

The endocrine system is composed of several endocrine glands. A ductless gland is called endocrine gland. Endocrine gland secretes its product directly into the bloodstream.

Hormones are produced in the endocrine glands. Hormone is mainly composed of protein. Hormones assist the nervous system in control and coordination.

Nerves do not reach to every nook and corner of the body and hence hormones are needed to affect control and coordination in those parts. Moreover, unlike nervous control, hormonal control is somewhat slower.

Glands and Hormones

Pituitary gland

• Also known as the master gland
• Situated at the base of brain
• Hormones: Growth hormone (GH), thyroid stimulating hormone (TSH), Follicle stimulating hormone (FSH)
• Functions: GH stimulates growth, TSH stimulates functioning of thyroid gland, FSH stimulates the follicles during ovulation.

Thyroid Gland

• Situated in the Neck
• Hormone: Thyroxine
• Function: Controls general metabolism and growth in the body.

Adrenal gland

• Situated above kidneys
• Hormone: Adrenalin
• Function: Prepares the body for emergency situations and hence is also called Fight and flight hormone.

Pancreas

• Situated near stomach
• Hornome: Insulin
• Function: Controls blood sugar level

Testis (in Male)

• Situated in scrotum
• Hormone: Testosterone
• Function: Stimulates sperm production, development of secondary sexual characters during puberty.

Ovary (in Female)

• Situated near uterus
• Hormone: Oestrogen
• Function: Egg production, development of secondary sexual characters during puberty.

Coordination in Plants

Unlike animals, plants do not have a nervous system. Plants use chemical means for control and coordination. Many plant hormones are responsible for various kinds of movements in plants.

Movements in plants can be divided into two main types, viz. tropic movement and nastic movement.

Tropic Movement

The movements which are in a particular direction in relation to the stimulus are called tropic movements. Tropic movements happen as a result of growth of a plant part in a particular direction. There are four types of tropic movements, viz. geotropic, phototropic, hydrotropic and thigmotropic.

Geotropic Movement

The growth in a plant part in response to the gravity is called geotropic movement. Roots usually show positive geotropic movement, i.e. they grow in the direction of the gravity. Stems usually show negative geotropic movement.

Phototropic Movement

The growth in a plant part in response to light is called phototropic movement. Stems usually show positive phototropic movement, while roots usually show negative phototropic movement.

If a plant is kept in a container in which no sunlight reaches and a hole in the container allows some sunlight, the stem finally grows in the direction of the sunlight.

This happens because of a higher rate of cell division in the part of stem which is away from the sunlight. As a result, the stem bends towards the light. The heightened rate of cell division is attained by increased secretion of the plant hormone auxin in the part which is away from sunlight.

Hydrotropic Movement

When roots grow in the soil, they usually grow towards the nearest source of water. This shows a positive hydrotrophic movement.

Thigmotropic Movement

The growth in a plant part in response to touch is called thigmotropic movement. Such movements are seen in tendrils of climbers. The tendril grows in a way so as it can coil around a support. The differential rate of cell division in different parts of the tendril happens due to action of auxin.

Nastic Movement

The movements which do not depend on the direction from which the stimulus acts are called nastic movement.

For example, when someone touches the leaves of mimosa, the leaves droop. The drooping is independent of the direction from which the leaves are touched.

Such movements usually happen because of changing water balance in the cells. When leaves of mimosa are touched, the cells in the leaves lose water and become flaccid, resulting in drooping of leaves.

Some Plant Hormones

• Auxin, gibberellins and cytokinin promote growth in plant parts.
• Abscissic acid inhibits growth in a particular plant part.

Summary

• Endocrine System: It is composed of ductless glands. Endocrine glands secrete various hormones, which are responsible for chemical coordination in the body.
• Plant Hormones: Some hormones promote growht, while some others inhibit growth.
• Tropic Movements: Growth or movement of plant parts in response to external stimuli. Growth is in particular direction.
• Nastic Movements: Movements of plants parts, are independent of direction, i.e. there is not specific direction of movement.