Biology 103 - Main points/Questions

1. Remember Plant Hormones?

2. What are the major human endocrine

glands?

3. What hormones do you need to know?

4. How are hormones controlled?

• In Summer plants need to balance root and shoot growth - too much of either is a waste of resources. Do you remember how they do this?

shoot tipgradient of auxin

(high)

(low)

(high)

gradient of cytokinin

• plants need to balance root and shoot growth – use AUXIN & CYTOKININ amounts

positive phototropism – controlled by …?

Light!

AUXIN!

• In fall plants need to respond to changing environmental cues to trigger leaf senescence (death).

Figure 24.14 The effects of ethylene

Hormone Signals in Animals

• Used for longer term signals than neurons

• Different cells respond to different hormones

• Hormones often key for homeostasis

33.02 The Timescale over Which Chemical Messengers

Work• CD33020.GIF

There are three big advantages to using chemical hormones as messengers rather than speedy electrical signals (nervous)

1. chemical molecules can spread to all tissues via the blood

2. chemical signals can persist much longer than electrical ones

3. many different kinds of chemicals can act as hormones

Balancing water concentration• The concentration of the urine is

regulated to maintain homeostasis• Hormones are key signaling molecules in

this process.

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• Negative feedback loops fight dehydration..

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• As you dehydrate you get thirsty (this is controlled by the nervous system)

• Your body also releases a hormone ADH that signals to the kidneys.

Where does water get reabsorbed in the kidney?

The 5 steps of urine formation

1. Pressure Filtration

2. Reabsorption of water

3. Selective reabsorption

4. Secretion

5. More water reabsorption

Further reabsorption of water

• Final step that balances water amounts

• Water can be variably reabsorbed into blood from collecting duct

• waters ability to be reabsorbed is controlled by a hormone called ADH – how?

Hormone signaling is a series of simple steps

1. issuing the command – release of the hormone from a gland

• Issuing the command

Hormone signaling is a series of simple steps

1. issuing the command

2. transporting the signal– most are transported through body by the

blood

• Transport

Hormone signaling is a series of simple steps

1. issuing the command

2. transporting the signal

3. hitting the target– hormone binds to a receptor on the target cell

• “hit the target”

Hormone signaling is a series of simple steps

1. issuing the command

2. transporting the signal

3. hitting the target

4. having an effect– After binding the receptor protein changes

shape and triggers a change in cell activity

Two basic categories of hormones

• ADH is a peptide hormone (remember a peptide bond?– Built of amino acids

• The other class of hormones are steroid based– Steroids are lipids so can pass through

membranes!

NUCLEUS

Signalreceptor

(a) (b)

TARGETCELL

Signal receptor

Transportprotein

Water-solublehormone

Fat-solublehormone

• Peptide based– Bind to receptor

on membrane

• Steroid– Transported

attached to a protein

– Bind to receptor inside the cell

Signalreceptor

TARGETCELL

Signal receptor

Transportprotein

Water-solublehormone

Fat-solublehormone

Generegulation

Cytoplasmicresponse

Generegulation

Cytoplasmicresponse

OR

(a) NUCLEUS (b)

• Peptide based– Signals are

often more transient (just in the cytoplasm)

– May alter gene expression

• Steroid– Mostly alter

gene expression

– Tend to be long lasting effects

Hormones are produced in

glands throughout your

body

Coordination of Endocrine and Nervous Systems in Vertebrates

• The hypothalamus receives information from the nervous system and initiates responses through the endocrine system

• Attached to the hypothalamus is the pituitary gland composed of the posterior pituitary and anterior pituitary

• The posterior pituitary stores and secretes hormones that are made in the hypothalamus

• The anterior pituitary makes and releases hormones under regulation of the hypothalamus

The posterior pituitary contains cells that originate in the hypothalamus

The hypothalamus and the posterior pituitary are connected by a tract of neurons

• hormones are made by cell bodies in the hypothalamus & moved to posterior pituitary– antidiuretic hormone (ADH) regulates the

kidney’s retention of water– oxytocin initiates uterine contractions during

childbirth and milk release in mothers

The anterior pituitary is a complete gland that produces the hormones that it secretes

The Hypothalamus and the Pituitary

The hypothalamus controls production and secretion of the anterior pituitary hormones by means of a family of special hormones

• neurons in the hypothalamus secrete releasing hormones

• they travel to the anterior pituitary through a special capillary system,

Portal system of the anterior pituitary gland and hypothalamus

The Anterior Pituitary

Secretes seven different hormones some you already know about…

• LH & FSHSome that are new to you…• TSH & GH

Pituitary hormones

• Follicle-stimulating hormone (FSH) – in females, it triggers the maturation of egg

cells and stimulates the release of estrogen– in males, it regulates sperm development

• Luteinizing hormone (LH)– in females, it triggers ovulation of a mature egg– in males, it stimulates the gonads to produce

testosterone

Control by hypothalamus Inhibited by combination of estrogen and progesterone

Stimulated by high levelsof estrogen

Inhibited by low levels of estrogen

Hypothalamus

GnRH

Anterior pituitary

FSH LH

Pituitary hormonesin blood

LH

FSH

FSH and LH stimulatefollicle to grow

LH surge triggersovulation

Ovarian cycle

Growing follicle Maturingfollicle

Corpusluteum

Degeneratingcorpus luteum

Follicular phase Ovulation Luteal phase

(a)

(b)

(c)

Da

ys

0 5 10 14 15 20 25 28| | | | | | | |

–

–

+ Estrogen

production

feeds back on

the signal

that drives

estrogen

release

• growth hormone (GH) – simulates the growth of muscle and bone

throughout the body

• Thyroid stimulating hormone (TSH) – Stimulates thyroid to produce thyroxin – a key

control of metabolism

• Negative feedback (feedback inhibition) controls how target gland hormones in the anterior pituitary are produced

• when enough of the target hormone has been produced, the hormone then feeds back to the hypothalamus and inhibits the release of stimulating hormones from the hypothalamus and the anterior pituitary

• Thyroxine – Modifies

metabolic rate– Requires iodine

• What if you don’t have enough iodine?

Fig. 35.11.b

Hormones are key players in maintaining homeostasis

• Commonly used as signals in negative feedback loops

• Remember Insulin & Glucagon?

Insulin and Glucagon: Control of Blood Glucose

• Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis

• The pancreas has clusters of cells that produce glucagon and insulin

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

Glucagon

STIMULUS:Blood glucose level

falls.

Alpha cells of pancreasrelease glucagon.

Liver breaksdown glycogenand releasesglucose.

Blood glucoselevel rises.

STIMULUS:Blood glucose level

rises.

Beta cells ofpancreasrelease insulininto the blood.

Liver takesup glucoseand stores itas glycogen.

Blood glucoselevel declines.

Body cellstake up moreglucose.

Insulin

Control of Blood Calcium

• Two antagonistic hormones regulate calcium (Ca2+) in the blood of mammals– Parathyroid hormone (PTH) causes blood

calcium levels to increase

– Calcitonin causes blood calcium levels to decrease.

• PTH increases the level of blood Ca2+

– It releases Ca2+ from bone and stimulates reabsorption of Ca2+ in the kidneys

– It also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food

• Calcitonin decreases level of blood Ca2+

– It stimulates Ca2+ deposition in bones and secretion by kidneys

Blood Calcium level(about 10mg/100ml)

Increasing Blood Calcium level

Decreasing Blood Calcium level

Draw the two negative feedback loops that involve these two hormones

Calcium Regulation• What happens when calcium levels drop?

• Parathyroid hormone (PTH) is secreted & causes bone cells to release calcium from the bones

• PTH also stimulates calcium reabsorption by the kidneys and absorption by the gut

• So dropping Ca++ leads to raising Ca++

PTH

Parathyroid gland(behind thyroid)

STIMULUS:Falling blood

Ca2+ level

Homeostasis:Blood Ca2+ level

(about 10 mg/100 mL)

Fig. 45-20-2

PTH

Parathyroid gland(behind thyroid)

STIMULUS:Falling blood

Ca2+ level

Homeostasis:Blood Ca2+ level

(about 10 mg/100 mL)

Blood Ca2+ level rises.

Stimulates Ca2+

uptake in kidneys

Stimulates Ca2+ release from bones

Increases Ca2+ uptake in intestines

Activevitamin D

Calcium Regulation• What happens when calcium levels rise?

• Calcitonin is secreted & causes bone cells to sequester calcium in the bones

• Calcitonin also slows calcium reabsorption by the kidneys

• So raising Ca++ leads to falling Ca++

Hormonal control of calcium homeostasis in mammals

What do you need to know?• Control Systems - Hormones: • List major plant hormones and their roles.• Explain how the two basic classes of animal

hormones have their effects on a cell.• Describe antagonistic hormones and explain how

they work together to maintain homeostasis.• List some major human hormones (certainly you

should know ADH, insulin, glucagon, calcitonin & PTH and you should be familiar with FSH, LH, estrogen, and progesterone), where they are produced and their roles.

Non-mammal Hormones• In insects, hormonal secretion influence both

metamorphosis and molting• prior to molting, neurosecretory cells on the surface

of the brain secrete brain hormone• brain hormone then stimulates a gland in the thorax

to produce molting hormone (ecdysone)• juvenile hormone is produced in the brain and

determines the result of a particular molt– when juvenile hormone levels are high, the molt produces

another larva

• Juvenile hormone promotes retention of larval characteristics

• Ecdysone promotes molting (in the presence of juvenile hormone) and development (in the absence of juvenile hormone) of adult characteristics

Ecdysone

Prothoracicgland

Brain

PTTH

EARLYLARVA

Neurosecretory cells

Corpus cardiacum

Corpus allatum

Juvenilehormone(JH)

Ecdysone

Brain

PTTH

Juvenilehormone(JH)

EARLYLARVA

Neurosecretory cells

Corpus cardiacum

Corpus allatum

LATERLARVA

Prothoracicgland

Ecdysone

Brain

PTTH

EARLYLARVA

Neurosecretory cells

Corpus cardiacum

Corpus allatum

LATERLARVA PUPA ADULT

LowJH

Juvenilehormone(JH)

Prothoracicgland

The hormonal control of metamorphosis