Endocrine system.pdf, Study notes of Biological Sciences

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BY

Ms Saira Manzoor Assistant Prof UNC-UOS

Objectives

By the end of the lecture, students should be able to:

• Classify endocrine glands and explain their structural and functional organization.
• Describe mechanisms of hormone action and feedback regulation.
• Explain functions of the hypothalamus and pituitary hormones with mechanisms.
• Summarize functions of:
  • Pituitary hormones
  • Thyroid and parathyroid glands
  • Calcitonin in calcium regulation
• Discuss thyroid, parathyroid, and calcitonin roles in calcium metabolism.
• Explain adrenal gland hormones and their physiological effects.
• Describe endocrine functions of pancreas and regulation of blood glucose.
• Explain endocrine role of kidney and physiology of growth.

CELL-TO-CELL SIGNALING

• Cell to cell signaling refers to the transfer of information from one cell to another. It is also called cell signaling or intercellular communication.
• The cells of the body communicate with each other through some chemical substances called chemical messengers.

Classification of Chemical Messengers

Conti….

➢ Endocrine glands secrete their products ( hormones ) into the extracellular space around the secretary cells.

• The secretions diffuse into capillaries and are carried throughout the body by the circulatory system

ENDOCRINE GLANDS

• Endocrine glands are the glands which synthesize and release the classical hormones into the blood.
• Endocrine glands are also called ductless glands because the hormones secreted by them are released directly into blood without any duct.

Hormones

• Hormones are chemical messengers, synthesized by endocrine glands.

Hypothalamus

• The hypothalamus is a small, vital midline organ located deep in the brain.
• It regulates several key physiological processes, including pituitary hormone release , body temperature, and appetite.
• The hypothalamus is organised into three major regions, each containing several nuclei (clusters of neuronal cell bodies).

Hypothalamus–pituitary axis

• The hypothalamus–pituitary axis is the central regulatory link between the nervous system and the endocrine system, responsible for maintaining hormonal balance and homeostasis.
• The hypothalamus secretes releasing and inhibiting hormones (e.g., TRH, CRH, GnRH, GHRH, somatostatin) which act on the anterior pituitary through the hypothalamo-hypophyseal portal system. In response, the anterior pituitary releases tropic hormones such as TSH, ACTH, GH, LH, FSH, and prolactin , which regulate target endocrine glands.
• This axis functions mainly through negative feedback mechanisms

Pituitary Gland

• The pituitary gland , or hypophysis , is an endocrine gland about the size of a pea and weighing 0.5 grams (0.018 oz) in humans.
• It is not a part of the brain. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity (sella turcica)

Conti….

• The pituitary is functionally connected to the hypothalamus by the a small tube called the infundibular stem.
• The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid bone in the middle cranial fossa at the base of the brain.