1. How our bodies maintain homeostasis.
The Endocrine System
How our bodies maintain homeostasis.

2. Learning Objectives
1. To determine how positive and negative feedback loops maintain homeostasis.
2. To determine the different glands involved in the endocrine system.

3. I. What is the Endocrine System?
Made of glands that produce and secret hormones (chemical messengers) into the bloodstream.
Regulation of growth, metabolism, and sexual development.
Responses to stress and injury.
Works together with the Nervous System to maintain internal balance (homeostasis).

5. II. What are glands and hormones?
Glands are organs that produce and release hormones into the bloodstream to act on a specific target cell.
Found in many areas of the body.
Hormones are chemicals released into the bloodstream and effect cells in other parts of the body (target cells).
Help the body to grow, develop, and maintain homeostasis.

7. Hormone Action
Steroids- insoluble in water, carried in the blood and released near the vicinity of the target cell.
Nonsteroid Hormones
Prostaglandins- act locally, affecting organ only where they are produced.

8. III. Control of Hormonal Secretions
Homeostasis is the regulation and maintenance of an internal environment (temperature, fluids, salts, pH, nutrients, gases) within the narrow ranges that support human life.
Receptors, brain, nerves (nervous system) and hormones (endocrine system) work together to maintain homeostasis in what is called a feedback loop.

9. What are Feedback Loops?
Feedback Loops: Information moves continuously from sensory receptors  brain  target (organs, tissues, or cells).
The presence or absence of hormones will trigger attempts by the body to regulate body conditions.

10. Negative Feedback Loops
The brain counteracts any change in the body that moves conditions above or below normal (set point).
Temperature, pH, fluids, nutrients, etc.
Maintains homeostasis by reversing or changing conditions back to normal.

11. Example
Hypothalamus (releasing hormone)  Pituitary Gland (stimulating hormone)  Target Gland (secretes hormone)  Hormone levels rise and releasing hormone is shut down.

12. Positive Feedback Loop
Brain uses information from receptors to increase the rate of change away from normal.
Examples: milk production, contractions during childbirth, blood clotting following a cut, fruit ripening.

13. Diabetes Sometimes feedback mechanisms go bad…
In Type II Diabetes cells become resistant to insulin; they no longer respond to it (won’t allow sugar to enter cell).
In Type I Diabetes the pancreas fails to produce insulin
High glucose levels in the blood can cause damage to many of the body’s systems and cells

14. Negative or Positive Feedback Loop?
During puberty, increase in release of certain growth hormones.
Positive Feedback Loop
You take a long hike in hot weather. You sweat to cool down body temperature.
Negative Feedback Loop

15. Negative or Positive Feedback Loop?
Lactation (producing milk): suckling action leads to the production of prolactin (hormone), which leads to more lactation.
Positive Feedback Loop
Blood sugar becomes too high, body creates more insulin to bring sugar levels back to normal.
Negative Feedback Loop

16. Negative or Positive Feedback Loop?
You are stuck in a cold cave. You shiver to warm the body temperature.
Negative Feedback Loop
Birth: Labor contractions push baby against cervix. This triggers productions of oxytocin (hormone), which triggers stronger contractions.
Positive Feedback Loop

17. IV. Human Endocrine Glands

18. Pineal Gland
Hypothalamus
Pituitary Gland
Thyroid Gland
Thymus
Adrenal Glands
Pancreas
Ovary
Testis

19. Website:
kidshealth.org/teen/your_body/bod y_basics/endocrine.html Your job- look at each of the hormones secretes by the glands and their functions.

20. 1. Hypothalamus-
Where the nervous system and endocrine system connect.
Detects stimulus and produces releasing hormones that stimulate other glands to release their hormones (usually with the aid of the pituitary gland).

22. Growth hormone-releasing hormone (GHRH): causes pituitary gland to release growth hormone.
Gonadotropin-releasing hormone (GnRH): causes gonads (ovaries and testes) to release hormones that control the reproductive system.

23. Human Endocrine Glands
2. Pituitary Gland (Master Gland)-
Located at base of brain, just beneath the hypothalamus.
It is often called the “master gland” because it makes hormones that control several other endocrine glands.
Secretes eight hormones that directly regulate many body functions and controls actions of several other endocrine glands.
Divided into anterior and posterior sections.

25. A. Growth Hormone (GH): stimulates cell division, protein synthesis, and bone growth in multiple tissues.
B. Prolactin (PRL)- Stimulates milk production from woman’s breast after childbirth and can affect sex hormone levels in reproductive organs.
C. Thyrotropin (Thyroid- Stimulating Hormone= TSH)- Stimulates the thyroid gland to make thyroid hormones.

26. D. Corticotropin (Adrenocorticotropin - ACTH)- stimulates production of cortisol (stress hormone) by the adrenal glands.
E. Antidiuretic Hormone (ADH): causes the blood to absorb water from kidneys.
F. Oxytocin- Causes milk letdown in nursing mothers and contractions during childbirth.

27. G. Luteinizing Hormone (LH)- Regulates sex hormone levels
and
Follicle-stimulating hormone (FSH)- promotes sperm production in men and stimulates ovaries to release egg in females.

28. 3. Thyroid Gland-
Major role in regulating the body’s metabolism (body’s ability to break down food and use it for energy).
A. Thyroxin and Triiodothyronine: increases metabolism, digestion, and energy levels by increasing rate cells release energy from carbohydrates.
B. Calcitonin: causes the body to remove calcium from the blood and increase bone formation.

30. Thyroid Diseases
Hypothyroidism (cretinism in infants):= underactive thyroid
Stunted growth, sluggishness, weight gain in adults.
Hyperthyroidism (Grave’s disease)= overactive thyroid- produces too much thyroxin.
Restlessness, weight loss, anxiety, can cause Goiter (enlarged thyroid).

32. 4. Thymus:
Releases the hormone Thyosin- causes white blood cells (T-lymphocytes) to reproduce and mature= immune system.

33. 5. Adrenal Gland:
Located on the Kidneys.
Release hormones that help the body prepare for and deal with stress.
A. Cortisol/Corticosteroids: influence and regulate salt and water balance, body’s response to stress, maintains blood pressure, metabolism, immune systems, and sexual development.

34. B. Epinephrine (and Norepinephrine): for energy and intense activities- increases blood pressure and heart rate when body experiences stress.
Aldosterone: maintain blood pressure
Sex Hormones: male (androgens) and female (estrogen) functions.

35. Adrenal Disorders
Cushing’s Syndrome (hypersecretion of cortisol)- blood glucose remains high, retains too much sodium, puffy skin, masculinizing effects in women.
Addison’s Diseases (hyposecretion)- decreased blood sodium, dehydration, low blood pressure, increased skin pigmentation.

36. 6. Pineal Gland:
A. Melatonin: helps regulate when you sleep at night and when you wake in the morning.

37. 7. Reproductive Glands:
Males= Testes: secretes male sex hormone:
Testosterone: causes sexual maturation, including sperm production, and male characteristics, such as facial hair and a deep voice.

38. Females= Ovaries: secretes female sex hormones:
a. Estrogen and Progesterone: causes sexual maturation including: egg production, menstruation and female characteristics, such as breast development, fat distribution and widening of hips.

39. 8. Pancreas:
Large organ behind stomach
Insulin- uptake of glucose into cells to make energy
and
Glucagon- Maintain steady levels of glucose in the blood

40. Example: Negative Feedback Loop: Body temperature is too low
Stimulates Pituitary Gland (master)
Receptors stimulate hypothalamus (brain)
Cold Exposure
STOP
Secretes hormone to stimulate thyroid gland
Thyroid gland secretes thyroxin (hormone)
Warms the body (increases energy and shiver)