Biology 30



Endocrine System

Section 13.1 – The Glands and Hormones of the Endocrine System

Main Function:

• To control and regulate all important aspects of life-growth

o Physical and mental development, maintenance and reproduction

Characteristics:

• More diffuse, less rapid and more prolonged effect than the nervous system

• Pituitary gland is referred to as the “master gland”- controls the endocrine system as brain controls the nervous system

o Both systems are coordinated by the hypothalamus

• Does not have its own transport system- works by using the circulatory system’s blood vessels to transport its chemical messengers – called hormones

• Endocrine glands are different from exocrine glands in that they release hormones and secrete these substances directly into the blood

• Exocrine glands produce secretions released via tubular ducts (ex: mammary glands secrete milk through ducts and therefore they are considered exocrine)

Hormones:

• Biochemical molecules of two general types- steroid (Estrogen, testosterone, progesterone) or protein (ADH, Insulin)

• Produced by endocrine glands and secreted directly into the blood

• Can stimulate other glands to secrete their hormones

• Exert their control by influencing/modifying enzyme activity or by changing the permeability of a membrane for a particular molecule

• Act only with certain target cells- which have receptor molecules in or on them for particular hormones (An example of Lock and Key Principle)

Look at the diagram below. Compare and contrast protein (amino acids) and steroid (lipid) hormones. See p.439-441 of your text.

Homeostasis:

• Tendency to maintain a constant internal environment

• Maintenance of this internal steady state is most important – if it fails illness or death

• To keep within healthy parameters, our body needs to be able to respond appropriately to change

Control System:

• Internal environment must be kept in constant equilibrium with respect to temperature, chemical composition, number of blood cells, among other things- if life is to continue

• Each organism receives stimuli from its external and internal environment and it must respond to such stress in a self-preserving way. To do this, organisms require a control system

Feedback Loops:

• There are two types of Feedback loops: Positive and Negative

• Negative: The stimulus is received, change is effected, system is shut down

• Positive: Stimulus is responded to but system is never shut down

Some Factors included in homeostasis are:

• Heartbeat

• Blood Pressure

• Respiration Rate

• Amount of CO2 and O2

• Calcium Level

• Blood Glucose Level

• Hormone Level

Negative Feedback

Response made by the control system is returned as a new stimulus to the system and negates the original response.

Eg: CO2 Concentration

Postivie Feedback Loop

In contrast to negative feedback, positive feedback is relatively uncommon in the human body. In positive feedback a change in the homeostatic condition is detected by receptors and the information is transmitted to the control center. The control center activates effectors which generate a response which increases the stimulus further reinforcing the initial change. Thus, positive feedback acts to reinforce or strengthen the stimulus or change.

Example in Humans = Oxytocin - During normal conditions the uterine muscle is not contracting. Dilation of the cervix triggers stretch receptors which transmit nerve impulses to the brain (hypothalamus). Stimulation of the hypothalamus results in oxytoxin (OT) being released from the posterior pituitary. Oxytocin is carried by the blood to the uterus where it causes uterine contractions. During the birth process dilation of the cervix initiates the release of OT which causes uterine muscle contractions. The uterine contractions begin to force the fetus through the cervix. As the fetus is pushed through the cervix this further stretches the cervix which results in more oxytocin being released. This positive feedback will continue until the baby has cleared the birth canal and the cervix is no longer stretched. [pic]

Section 13.2 – Hormonal Regulation of Growth, Development, and Metabolism

Pituitary Gland

• Located in the brain

• Responds to nervous stimulation and chemical releases from the hypothalamus

• Divided into posterior and anterior lobes – each one releasing a variety of hormones into the blood

Posterior Lobe:

Stores and secretes two hormones produced by the hypothalamus, which have traveled to the pituitary via specialized nerve cells

a) Antidiuretic Hormone (ADH)

• Targets the kidneys

• Controls the reabsorption of water by the kidney tubules during the formation of urine

• Raises the blood pressure by constricting blood vessels

• Also called vasopressin

b) Oxytocin

• Targets the mammary glands and uterus

• Stimulates the contraction of smooth muscles of the uterus during labor

• Stimulates the ejection of breast milk

Anterior Lobe:

Produces its own hormones but their release is regulated by the hypothalamus

• Hormones released from hypothalamus → transported in blood to the pituitary →pituitary releases required hormones → hormones move to target tissues/organs/cells

a) Growth Hormone (GH)

• Targets most cells

• Promotes growth by increasing cell division

• Disorder related to GH include:

1. ↑ production before growth plates fuse : Gigantism

2. ↑ production after growth plates fuse : Acromegaly (wide fingers, face, ↑ bone width)

3. ↓ production before growth plates fuse: Dwarfism

b) Thyroid Stimulating Hormone (TSH)

• Targets thyroid gland, stimulating it to release thyroxin which regulates body metabolism and helps develop the nervous system

c) Adrenocorticotropic Hormone (ACTH)

• Targets the adrenal glands

o Adrenal Cortex: Produces three different hormones – aldosterone (water balance): cortisol (Balances glucose by doing protein and carb. metabolism) and Sex hormones

d) Prolactin (PRL)

• Targets the mammary glands

• Stimulates the Production of milk

• Also promotes uterine contractions

e) Gonadotropic Hormones- hormones released which target the testes in males and the ovaries in females

• Follicle Stimulating Hormone (FSH): Stimulates the maturation of the egg and the production of sperm

• Lutenizing Hormone (LH): Stimulates ovulation in females and the production of testosterone in males

A Closer Look….

The Thyroid Gland

Two lobes of tissue that are joined by a narrow portion (looks like a

• bowtie)

• Lies over the trachea

• Releases thyroid hormone Thyroxin (iodine containing)

• Regulates overall basal metabolic rate

• Important in bodily growth

• Controls the development of the nervous system

Effect of the Thyroid

• Directly or indirectly affects every tissue of the body

• Increases the body’s metabolic rate (O2 consumption to produce energy)

o By product of this reaction is heat and therefore the body feels warmer

o Other factors that contribute to metabolic rate are exercise, food intake, muscle tone, etc.

• Stimulates the secretion of GH and promotes its effect on synthesis of proteins

• Required for the development of the CNS in children and for normal CNS activity in adults

• Calcitonin: responsible for decreasing blood calcium levels by increasing storage in bones and teeth, increasing excretion in kidneys, and decreasing absorption in intestines.

• 65% of thyroid secretions are thyroxin

Disorders attributed to the Thyroid Gland:

o Normal thyroid function is called : euthyroidism

o Hypothyroidism: deficient hormone secretion

o Causes:

▪ Thyroid gland fails

▪ Not enough iodine in diet

▪ TSH hormone deficiency

o Results:

▪ Reduced metabolic rate – intolerant to cold, weight gain, diminished alertness, easily fatigued

▪ Myxedema: water retained due to slow metabolism resulting in a puffy appearance of the feet, face and hands.

o Disorders:

▪ Cretinism: Hypothyroidism from birth causes dwarfism and possible mental retardation

o Treatment:

▪ Hormone therapy

▪ More Iodine in diet (Dairy, Canned Veggies, seafood, cured meat)

o Hyperthyroidism: excess hormone secretion

o Causes:

▪ Grave’s disease – immune system attacks thyroid causing over production of thyroxin because it produces antibodies that cause the constant stimulation of TSH

o Result:

▪ Elevated metabolic rate – increased heat production, excessive perspiration, weight loss, weakness attributed with muscle loss

▪ Bulging eyes – reason still unknown

o Treatment:

▪ Removal of part of the thyroid gland

▪ Anti-thyroid drug which interfere with the hormone synthesis

o Goiter: results from an enlarged portion of the thyroid gland

May result from either hypothyroidism or hyperthyroidism

Parathyroid Gland

Four small glands embedded in the back of the thyroid gland

Secretes one hormone: PTH (parathyroid hormone) or (parathormone) when calcium levels in the blood are below normal

Increases calcium by:

* Increasing the # of bone-destroying cells, therefore releasing the calcium from storage in the bones

* Increasing calcium re-absorption in the kidneys

* Increasing the uptake in the digestive tract.

Works antagonistic to calcitonin

Disorders - Parathyroid

Tetany: not enough parathyroid hormone, low blood calcium – neurons depolarize without a stimulus, resulting in twitches, spasms and convulsions

Osteitis fibrosa cystica: too much parathyroid hormone, high blood calcium – softening and demineralization of bones, calcium deposits in kidneys and other organs

Section 13.3 – Hormonal Regulation of the Stress Response

The Adrenal Glands:

▪ 2 Adrenal Glands: one above each kidney

▪ 2 organs make up each one: adrenal medulla and adrenal cortex

Adrenal Medulla:

▪ Actually part of the Sympathetic Nervous System (part of ANS)

▪ Hormones are epinephrine and norepinephrine (Adrenaline/Noradrenaline)

▪ Part of the short term stress response

▪ Released as a response to stress-

o Glucose is released (glycogen is broken down)

o Heart Rate increases

o Breathing rate Increases

o Iris dilates and pupil gets larger

o Increased CNS alertness

o Increased blood Pressure (to ensure blood is getting to the vital organs)

o Other activities are inhibited (bladder, stomach)

Adrenal Cortex:

▪ Part of the long term stress response

▪ Secretes three types of steroid hormones:

o Aldosterone (mineralocorticoids)

o Cortisol (Glucocorticoids)

o Sex Hormones (in small amounts) (Gonadocorticoids)

Aldosterone:

▪ Retains Na+ and eliminates K+ during formation of urine

▪ Induces reabsorption of water by working on the distal tubule (Remember that water follows solute!!)

▪ Secretion is not only stimulated by the anterior pituitary’s release of ACTH but also by a rise in the K+ in the blood

o Disorders:

← Cushings: Increase production of Aldosterone

o Causes hypertension, increase BP, edema

← Addisons: Decrease production of Aldosterone

o Decrease in Blood Pressure, dehydration

Cortisol:

▪ Helps to resist and recover from stress

▪ Affects glucose levels by:

o Converting Amino Acids in the liver into carbohydrates when stores are depleted

o Inhibiting glucose uptake and use by certain tissues so it can be spared for the brain

o Stimulates protein degradation so amino acids are available for glucose production

o Breaks down lipids into free fatty acids, which other tissues can use for metabolism so that glucose can be saved for the brain

o Disorders:

← Cushings: Increase production of Cortisol

o Muscle wasting, hyperglycemia, obesity

← Addisons: Decrease production of Cortisol

o Poor injury recovery, hypoglycemia, weight loss

Sex Hormones:

▪ Small secondary sex characteristics

o Disorders:

▪ Addisons: Decrease production of Sex Hormones (Loss of pubic hair)

▪ Cushings: Increase production of sex hormones

Section 13.4 – Hormonal Regulation of Blood Sugar

Blood Sugar Regulation

After you eat, your blood sugar is raised…(HYPERGLYCEMIA)

o Pancreas (Beta Cells in Islets of Langerhans) secrete Insulin

o Insulin:

o Increases Permeability of cells to glucose

o Increase the rate of glucose to ATP

o Promotes the conversation of glucose to fat

o Converts glucose to glycogen in the Liver

o Overall Decrease of Blood Glucose Concentration

Hyperglycemia ( [blood sugar] (pancreas, islets if Langerhans, β cells

(“beta” cells)

Glucose to glycogen insulin into blood

• Promote conversation of glucose to fat

• Permability of cells to glucose

• Rate of ATP

When your blood sugar is low such as when you skip a meal…(HYPOGYCEMIA)

o Pancreas (Alpha Cells in the Islets of Langerhans) secrete Glucagon

o Glucagon:

o Converts glycogen to glucose in liver

o Overall Increase in Blood Sugar

Hypoglycemia ( [blood glucose] ( pancreas ( α cell “Alpha” cell ( glucagon ( liver

[pic] [blood glucose] ( Promotes glycogen, conversion to glucose in blood

Disorders:

o Diabetes Mellitus: Deteriorating B cells

o Inability to produce Insulin

o Symtoms:

▪ High Glucose in urine =”Sweet pee”

▪ Water follows solute and so increases urine output

▪ Causes thirst

▪ Tired/lethargic

▪ Increase in fat/protein metabolism

▪ Blood shunt to important organs

o Hyperinsulinism:

o Excess insulin in the body

o Low sugar level and can cause insulin shock

Hormone Control of the Gonads

o Gonads are the reproductive organs – testes and ovaries

o Onset of puberty marked by the hypothalamus releasing GnRH- Gonadotropin releasing hormone

o GnRH activates the pituitary gland which produces, stores and secretes two gonadotropic hormones

o FSH: Follicle Stimulating Hormone

o LH- Leutinizing Hormone

These hormones regulate the functions of the testes and the ovaries

| |In Males |In Females |

|FSH |Stimulates the production of sperm cells in|Stimulates the development of the follicle |

| |the seminiferous tubules |cells of the ovaries |

|LH |Promotes the production of two hormones |Stimulates ovulation and the formation of |

| |(testosterone and androsterone) in the |the corpus luteum |

| |interstitial cells | |

Both of the structures formed in the ovaries (Follicle cells and corpus luteun) in turn produce other hormones affecting female reproduction.

Testes

* Produces the hormone testosterone.

* Secretion of testosterone is stimulated by secretion of Interstitial Cell Stimulating Hormone (ICSH)

* Testosterone production causes the development of male secondary sex characteristics:

* Facial hair development, deepening of voice, muscle development, increased sex drive, increased secretion of body oils

Ovaries

* Produce the female hormones estrogen and progesterone

* Estrogen:

* Secretion of estrogen is stimulated by secretion of FSH from the pituitary

* Causes the development of female secondary sex characteristics:

* widening of pelvis (hips), breast development, thickening of inner uterus lining (endometrium)

• Progesterone:

* Secretion of progesterone is stimulated by the secretion of luteinizing hormone from the pituitary

* Maintains pregnancy:

* Inhibits follicle development and ovulation, Inhibits uterus contractions, Encourages the thickening of the uterus lining (endometrium)

We will spend more time on these hormones in the reproduction unit!

1.What structures in the pancreas serve an endocrine function?

2. What are the two hormones produced by the endocrine cells?

3.Which hormone would be secreted by the pancreas after a large meal?

4.Which hormone would be secreted in the morning if you decided to go jogging?

5. Predict why glucose would be present in the urine of dogs after the removal of the pancreas.

-----------------------

Outcomes

You will:

• Explain how the endocrine system contributes to homeostasis

• Identify the principal endocrine glands in the human body and the hormones they secrete

• Explain how the endocrine system allows the body to sense and respond to the internal environment

• Explain the relationship between negative feedback and hormonal regulation of the body

• Explain how the endocrine system is involved in seasonal affective disorder (SAD) and the sleep-wake cycle

[pic]

Homeostasis: is the steady state

Eg: Glucose Level

Increase in Physical Activity as Registered by the Brain

Increase in Breathing Movement (Diaphragm and Intercostals) Muscles)

Increase in CO2 Concentration in Blood

Do Section 13.1 Review page 442 # 1-5

Outcomes

You will:

• Describe the structures of the anterior and posterior pituitary and explain how they are regulated

• Explain how human growth hormone (hGH) contributes to healthy growth and development

• Evaluate the use of hormone therapy

• Describe the structures and regulation of the thyroid gland and its role in homeostasis

• Describe the physiological effects of hormonal imbalances

• Formulate a hypothesis about an environmental factor to which the endocrine system responds

Do Investigation 13.A page 447

• Prolactin, and GH are considered non-tropic hormones because they stimulate tissues other than endocrine glands

• All other anterior lobe hormones are considered tropic because they activate endocrine glands

Anterior Pituitary

Thyroid

All Body Cells to Increase Metabolism

TSH

Thyroxin

Do Section 13.2 Review page 450 # 1-7

Outcomes

You will:

• Explain how the nervous and endocrine systems act together to regulate the stress responses

• Identify and describe the actions of epinephrine and norepinephrine in the human body

• Describe the effects of cortisol and aldosterone on the human body during the long term stress response

• Describe the physiological effects of chronic stress or imbalance in hormones

•

So what does an EpiPen do?

Do Section 13.3 Review page 455 # 1-7

Outcomes

You will:

• Describe the structures of the pancreas and its role in homeostasis

• Explain how insulin and glucagons regulate levels of blood glucose

• Describe the physiological effects of diabetes and how the conditions occur

• Analyse data and infer the role of various hormones based on observations

• Explain how science and technology are developed to meet societal needs and expand human capability

Do Thought Lab 13.1 p. 458

Do Section 13.4 Review page 462 # 1-5

Have you ever seen a patient in a hospital on intravenous? A bag of colorless fluid hangs on a PQRaÝî™

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Glucose is a common component of intravenous fluid. Its purpose is to provide energy for the body. Notice however that the glucose would not be entering the body through the digestive system but rather going directly through the blood. How is blood glucose used? This regulation is a vital homeostatic mechanism since glucose serves as a major fuel source for cellular respiration and is required for the synthesis of other important organic compounds. The hormone is insulin which is made in the pancreas. Before getting into the details of insulin and hormonal regulation of glucose metabolism, there is some background information you should know about the pancreas and the control mechanism of negative feedback.

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