Glands are studied as a part of human anatomy and physiology.
They are sac like tissue structures in the body which play a vital role in the physiology and homeostasis.
Anatomically they are made of secretory cells and also situated in safe yet prominent location inside the body.
Glands are quite numerous and regulate different physiological functions and activities.
The glands can be differentiated based on their locations, based on their type of secretions, based on the organ systems they control etc.
These glands mostly perform their function through release of secretions. These secretions can be hormones, enzymes and sometimes just fluid yet all of them have some important functions.
Without their secretions, there can arise enzyme and hormone deficiency diseases.
Based on the way of secretion: Glands are two types based on secretion as
1. Exocrine glands: They secrete into a location or region of the body through a duct and their secretions are called enzymes mostly while some are non enzymes.
Types of exocrine glands and their secretions include
- Salivary gland: In the buccal cavity secrete saliva. This saliva has many functions.
- Pancreas: Secretes enzyme amylase, trypsin and lipase. These enzymes digest carbohydrates, proteins and fats respectively.
- Sperm: Sperms produce Hyaluronidase an enzyme which helps it swim in the uterine tissue to reach ova.
- sweat glands: secrete sweat which acts to regulate body temperature and also excretion.
- Sebaceous gland: secrete sebum.
- Lachrymal glands: In eye secrete water to moisten the eye.
2. Endocrine glands: Secrete into blood flowing through them, so as to let the secretion function at distant parts of the body from the gland. They are ductless glands. Their secretions are called as hormones.
Based on their location there are broadly two types of endocrine glands viz.
a) Pituitary Gland (of hypothalamus): This is a gland located below the hypothalamus in the brain.
For more about anatomy refer to pituitary structure.
The gland is differentiated as anterior and posterior gland and has definite secretions for each type i.e.
i) Anterior pituitary gland: Located in the front part of pituitary
- Prolactin: Stimulates milk production in mothers.
- Somatotrophin: A hormone which regulates growth of the body and tissues.
- leutinising hormone: Stimulates ovulation (egg formation) in females and testosterone production in males.
- Thyroid stimulating hormone: Stimulates thyroid gland to produce T3 & T4 hormones.
- Adreno corticotrophic hormone: Stimulates secretion of glucocoticoids and mineralo corticoid hormones.
- Follicle stimulating hormone signals formation of estrogen and progesterone by female reproductive system.
ii. Posterior pituitary Present behind the front part of pituitary as shown in diagram above.
- vasopressin (anti-diuretic hormone) It controls water loss from kidneys. So minimises urine formation and saves water in the body.
- Oxytocin It signals uterus for delivery in pregnant women after period of gestation. It also stimulates milk secretion in mother.
b) Thyroid gland: Produces thyroid hormones T3 & T4.
c) Parathyroid gland: Produces parathormone.
Both thyroid and parathyroid glands are examples for types of glands in the neck.
d) Adrenal gland: located on the two kidneys. It has outer cortex and inner medulla regions.
- Cortex: secretes gluco-corticoids and mineralo-corticoids.
- Medulla: secretes nor-adrenalin. This is one of the neurotransmitters and is called as flight or fight hormone.
e) Pancreas: Pancreatic gland has both exocrine and endocrine functions. It secretes multiple hormones which control body glucose metabolism. Its endocrine function release secretions like insulin, glucagon, somatostatin.
f) Kidneys: produce Renin angiotensin (controls blood pressure).
g) Pineal gland: Located inside the brain and called as body natural clock. One ca see jet-lag effects due to its secretions. Melatonin (sleep hormone).
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h) Testes: Secrete Testosterone. Produced only in males to large extent and to very small extent in women. Signals male characters like beard, muscles etc.
i) ovaries: Produce Estrogen, progesterone. Secreted only in women and regulate reproduction cycle.
Reference: Principles of Anatomy and Physiology by Gerard J. Tortora
All the glands are located in distinct locations in the human body. They regulate the physiology to a large extent by receiving stimulus from the brain. So we can notice that those glands present in the brain secrete hormones which go outside the brain and act on other glands distributed in different parts of the body. They travel through blood to the target organs after being released.