Life Sciences Term 2

What is the endocrine system?

1: Terminology and definitions:

Biological term	Description
Endocrine glands	Ductless glands secreting hormones directly into bloodstream.
Exocrine glands	Secrete substances into ducts that lead into cavities in the body or lead directly to the external environment.  (Examples:  sweat glands, mammary glands, the liver, salivary glands and the pancreas.)
Hormones	Organic chemical messengers secreted directly into the blood by an endocrine gland.
Homeostasis	It is the process of maintaining a constant internal environment within narrow limits, despite changes that take place internally and externally.
Negative feedback mechanism	When there is an increase from normal, a corrective mechanism causes a decrease and vice versa to maintain a balanced system.

2: What is the endocrine system?

• Hormone	Gland	Location	Function
  Antidiuretic hormone (ADH)	Neurosecretory cells of the hypothalamus ADH is stored in the Pituitary gland	In the centre of the brain	Regulates osmoregulation in the kidneys (in the distil convoluted tubules and the collecting tubules)
  Thyroxin	Thyroid gland	Below the larynx in the neck region	·         Regulates the basal metabolic rate of the cells in the body ·         Affects growth and functioning of the heart and the nervous system ·         Stimulates growth and differentiation of tissue in a foetus and in children ·         Regulates the body temperature when stimulated by the hypothalamus
  Adrenalin (fight-and-flight hormone)	Adrenal gland	Above the kidney	Prepares the body to deal with stress: ·         Increase in heartbeat rate ·         Increase in breathing rate ·         Increase in blood pressure ·         Increase in muscle tone ·         Increase in blood sugar levels ·         Decrease in blood supply to the skin and digestive system ·         Causes pupils to dilate
  Aldosterone	Adrenal gland	Above the kidney	Helps the uptake of sodium ions in the loop of Henle in the kidneys
  Prolactin	Pituitary gland:	Base of the brain and attached to the hypothalamus	·         Stimulates the mammary glands to produce milk ·         Counteracts the effect of dopamine which is responsible for sexual arousal
  Oestrogen	Gonads: ovaries	Located in the lower abdominal region with each ovary located within the pelvic bones (in line with the ball-and-socket joints of the femurs)	·         Oestrogen promotes the development of the secondary sexual characteristics in females like breasts, the thickening of the endometrium (uterus) and the female body shape ·         Necessary for the process of ovulation ·         Oestrogen inhibits the secretion of FSH by the anterior pituitary gland so that only one follicle is produced during ovulation ·         High oestrogen levels will trigger the secretion of luteinising hormone (LH)
  Progesterone	Gonads: ovaries	Located in the lower abdominal region with each ovary located within the pelvic bones (in line with the ball-and-socket joints of the femurs)	·         Progesterone prepares the endometrium of the uterus for implantation once fertilisation of the egg cell has occurred ·         Necessary for the production of the mucus plug to prevent sperm or other substances from entering the uterus during pregnancy ·         Decrease in progesterone levels causes menstruation ·         Progesterone improves memory and cognitive ability
  Testosterone	Gonads: testes	Leydig cells in the testes of males located in the scrotum at the bottom of the pelvis	·         Testosterone is responsible for the secondary sexual characteristics in males like a deeper voice, pubic hair, hair on face ·         Necessary for the normal development of sperm ·         Activates genes in the cells of Sertoli to promote the differentiation of the spermatogonia
  Glucagon	Pancreas:  Islets of Langerhans	Endocrine cells of the pancreas	Controls the increase in the blood sugar level by causing the conversion of glycogen to glucose
  Insulin	Pancreas: Islets of Langerhans	Endocrine cells of the pancreas	·         Controls blood sugar by causing the conversion of glucose into glycogen ·         Inhibits the functioning of glucagon
  Growth hormone (somatotrophin)	Pituitary gland:	Base of the brain and attached to the hypothalamus	For growth, repair and replacement of cells
  Follicle stimulating hormone (FSH)	Pituitary gland:	Base of the brain and attached to the hypothalamus	In males: stimulates spermatogenesis In females: stimulates the development of the follicle for process of ovulation
  Luteinising hormone (LH)	Pituitary gland:	Base of the brain and attached to the hypothalamus	In males: stimulates the synthesis of the hormone testosterone by the Leydig cells in the testes In females: LH stimulates the release of the secondary oocyte from the Graafian follicle and then the development into the corpus luteum
  Thyroid- stimulating hormone (TSH)	Pituitary gland:	Base of the brain and attached to the hypothalamus	Stimulates the production of thyroxin by the thyroid gland
  Prolactin	Pituitary gland	Base of the brain and attached to the hypothalamus	Stimulates mammary glands to secrete milk

   

  The endocrine system works in conjunction with the nervous system.  The endocrine system is responsible for chemical coordination, regulating the functioning of all the organs in the body
  
• It consists of glands situated throughout the body
• These endocrine glands secrete organic chemical messengers called hormones in the bloodstream
  
• Hormones are organic substances and are mostly proteins, but a few are lipids (fats) (usually the sex hormones)
  
• Hormones are produced in small quantities
• They are carried in the blood stream to a target organ/tissue where they control the activities of a target organ to perform a specific  function
  
• Hormones work together as an integrated system where they either stimulate or inhibit organs.

3: The differences between the endocrine system and the nervous system

• The nervous system and endocrine system controls different types of activities in the body
• They are jointly responsible for the functioning of all the different organs and systems, this is known as coordination
• The nervous system co-ordinates very quick responses to external stimuli
• The endocrine system controls responses that are not that fast but are long-lasting and reflect the body’s internal environments.

Endocrine system	Nervous system
1.      Made up of glands 2.      Produces hormones 3.      Hormones are transported by the blood 4.      Effects are slower and more general 5.      Hormones control long-term changes (e.g. growth)	1.      Made up of nerves 2.      Produces nerve impulses 3.      Impulses are transmitted along the nerves 4.      Effects are very quick and very specific 5.      Nerve impulses control short-term changes (e.g. sneezing, lifting your arm)

4: The differences between endocrine glands and the exocrine glands

Endocrine glands	Exocrine glands
Glands are ductless, secrete directly into bloodstream	Secrete their substances into ducts and not the bloodstream (think of the salivary glands secreting saliva in ducts that transport it to the mouth)
Secrete hormones	Does not secrete hormones

The pancreas is the only gland that is both exocrine (pancreatic juices for digestion) and endocrine (insulin and glucagon).

Diagram of the pancreas illustrating the islets which are the endocrine glands composed of alpha and beta cells. The exocrine glands are represented by the acinar cells that secrete digestive enzymes .  Source: http://pathology.jhu.edu/pancreas/basicoverview3.php?area=ba

It is strongly suggested that learners have to know the following diagram well. This is a snapshot of all the relevant glands, with the hormones they secrete and the function of each hormone:

SNAPSHOT of human endocrine system

Hormone	Gland	Location	Function
Antidiuretic hormone (ADH)	Neurosecretory cells of the hypothalamus ADH is stored in the Pituitary gland	In the centre of the brain	Regulates osmoregulation in the kidneys (in the distil convoluted tubules and the collecting tubules)
Thyroxin	Thyroid gland	Below the larynx in the neck region	Regulates the basal metabolic rate of the cells in the body Affects growth and functioning of the heart and the nervous system Stimulates growth and differentiation of tissue in a foetus and in children Regulates the body temperature when stimulated by the hypothalamus
Adrenalin (fight-and-flight hormone)	Adrenal gland	Above the kidney	Prepares the body to deal with stress: Increase in heartbeat rate Increase in breathing rate Increase in blood pressure Increase in muscle tone Increase in blood sugar levels Decrease in blood supply to the skin and digestive system Causes pupils to dilate
Aldosterone	Adrenal gland	Above the kidney	Helps the uptake of sodium ions in the loop of Henle in the kidneys
Prolactin	Pituitary gland:	Base of the brain and attached to the hypothalamus	Stimulates the mammary glands to produce milk Counteracts the effect of dopamine which is responsible for sexual arousal
Oestrogen	Gonads: ovaries	Located in the lower abdominal region with each ovary located within the pelvic bones (in line with the ball-and-socket joints of the femurs)	Oestrogen promotes the development of the secondary sexual characteristics in females like breasts, the thickening of the endometrium (uterus) and the female body shape Necessary for the process of ovulation Oestrogen inhibits the secretion of FSH by the anterior pituitary gland so that only one follicle is produced during ovulation High oestrogen levels will trigger the secretion of luteinising hormone (LH)
Progesterone	Gonads: ovaries	Located in the lower abdominal region with each ovary located within the pelvic bones (in line with the ball-and-socket joints of the femurs)	Progesterone prepares the endometrium of the uterus for implantation once fertilisation of the egg cell has occurred Necessary for the production of the mucus plug to prevent sperm or other substances from entering the uterus during pregnancy   Decrease in progesterone levels causes menstruation Progesterone improves memory and cognitive ability
Testosterone	Gonads: testes	Leydig cells in the testes of males located in the scrotum at the bottom of the pelvis	Testosterone is responsible for the secondary sexual characteristics in males like a deeper voice, pubic hair, hair on face Necessary for the normal development of sperm Activates genes in the cells of Sertoli to promote the differentiation of the spermatogonia
Glucagon	Pancreas:  Islets of Langerhans	Endocrine cells of the pancreas	Controls the increase in the blood sugar level by causing the conversion of glycogen to glucose
Insulin	Pancreas: Islets of Langerhans	Endocrine cells of the pancreas	Controls blood sugar by causing the conversion of glucose into glycogen Inhibits the functioning of glucagon
Growth hormone (somatotrophin)	Pituitary gland:	Base of the brain and attached to the hypothalamus	For growth, repair and replacement of cells
Follicle stimulating hormone (FSH)	Pituitary gland:	Base of the brain and attached to the hypothalamus	In males: stimulates spermatogenesis In females: stimulates the development of the follicle for process of ovulation
Luteinising hormone (LH)	Pituitary gland:	Base of the brain and attached to the hypothalamus	In males: stimulates the synthesis of the hormone testosterone by the Leydig cells in the testes In females: LH stimulates the release of the secondary oocyte from the Graafian follicle and then the development into the corpus luteum
Thyroid- stimulating hormone (TSH)	Pituitary gland:	Base of the brain and attached to the hypothalamus	Stimulates the production of thyroxin by the thyroid gland
Prolactin	Pituitary gland	Base of the brain and attached to the hypothalamus	Stimulates mammary glands to secrete milk