Homeostasis and Feedback Mechanisms

1. The Endocrine,
Nervous and
Reproductive System

2. Homeostasis and Feedback Mechanisms
 Homeostasis
 the balance state of internal conditions despite changes
in external environment
 different body systems complement one another to
create internal balance- homeostatic regulation

3. Homeostasis and Feedback Mechanisms
 Endocrine Glands – secrete hormones that help
regulate the activities of cells
 Stimulus- any external or internal change in the
environment
 External Stimulus- arises from outside the body
 Internal Stimulus- originates within the body
 Feedback mechanism/ feedback regulation- self-
adjusting mechanism

4. 2 Types of Feedback Mechanism
1. Negative feedback loop
- response reduces the stimulus until conditions
return to a homeostatic
state.

6. 2 Types of Feedback Mechanism
2. Positive feedback loop
- occurs when a response amplifies a
stimulus, which in turn elicits further
response.

8. Homeostasis and Feedback Mechanisms
 Neuroendocrine System- endocrine + nervous
system
 Hypothalamus- contains neurosecretory cells, sends
hormones.

9. Target cells
• Blood facilitates the circulation of hormones.
• Hormones are recognized by their target cells via
membrane receptors
• Molecular shape of the hormone should physically fit
the target cell’s receptor so that the hormone
receptor complex can initiate the response.

10. The Endocrine System

11. The Endocrine System
 chemical messengers (hormones)
 2 types of glands
 Endocrine glands
- Release their hormones directly into the
bloodstream
 Exocrine glands
- Release their secretion through ducts

13. Pituitary Gland and Hypothalamus
 Produce hormones and controls various glands
 close to the hypothalamus and is connected to the
blood vessels and nerves
 “Master Gland”
 Composed of the anterior and posterior lobe
 Posterior lobe
 extension of the hypothalamus
 antidiuretic hormone (ADH) & Oxytocin

15. Pituitary Gland and Hypothalamus
 Antidiuretic hormone (ADH)
 decreases the amount of urine exerted by the
kidneys
 Oxytocin
 promote “milk letdown”

16. Pituitary Gland and Hypothalamus
 Anterior lobe
 Secretes rolactin, gonadotropic hormones, thyroid-
stimulating hormone (TSH) and growth hormones.

17. Thyroid Gland
 located at the base of the neck
 thyroxine is converted into triiodothyronine,
the active form of thyroid hormone
 Calcitonin- lowers calcium levels
 Hypothyroidism- underactive thyroid gland,
decreases metabolic rate
- radioactive iodine treatment

19. Thyroid Gland
 Cretinism- physical and mental retardation
 Goiter- abnormal enlargement of the thyroid
gland
 Levothyroxine- a thyroid hormone

20. Parathyroid Gland
 at the back of the thyroid gland
 Parathormones
regulate calcium in the blood and oppose the
action of calcitonin
Enhance calcium absorption
Calcium ( muscle contraction, blood clotting and
others)

21. Adrenal Gland
 above the kidney
 inner part (adrenal medulla)
 outer part (adrenal cortex)

22. Adrenal Medulla
• epinephrine ( adrenaline) and norepinephrine
(norepinephrine)
• helps the body to respond to emergencies.
• Adrenaline – “emergency hormones”

23. Adrenal Cortex
• glucocorticoids, mineralocorticoids and sex
hormones
•First two, prolonged stress and mobilizing energy
reserves.
• Cortisol- helps body respond to stress.
• Aldosterone- regulates salt and water in the
body.

24. Pancreas
• located between the spleen and small intestine.
• produces digestive enzymes and hormones
• Islets of Langerhans- produce pancreatic amylase
• secrete insulin, glucagon and somatostatin
• Insulin- lowers blood sugar level
• Glucagon –rises blood sugar level
• Somatostatin- inhibits secretion of other hormones