E N D O C R I N E C H 4 5
R E P R O D U C T I O N C H 4 6
D E V E L O P M E N T C H 4 7
A N D H O W M U S C L E S C O N T R A C T

Overview: The Body’s Long-Distance Regulators

Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body
 Hormones reach all parts of the body, but only target cells are equipped to respond
 Insect metamorphosis is regulated by hormones

 Two systems coordinate communication throughout the body: the endocrine system and the nervous system
 The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior
 The nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells

Types of Secreted Signaling Molecules

Secreted chemical signals include





Hormones
Local regulators
Neurotransmitters
Neurohormones
Pheromones

 Exocrine glands have ducts and secrete substances onto body surfaces or into body cavities (for example, tear ducts)

Local Regulators
 Local regulators are chemical signals that travel over short distances by diffusion
 Local regulators help regulate blood pressure, nervous system function, and reproduction
 Local regulators are divided into two types

Paracrine signals act on cells near the secreting cell

Autocrine signals act on the secreting cell itself

Fig. 45-2a
Blood vessel
(a) Endocrine signaling
Response
(b) Paracrine signaling
(c) Autocrine signaling
Response
Response

Neurotransmitters and Neurohormones
 Neurons (nerve cells) contact target cells at synapses
 At synapses, neurons often secrete chemical signals called neurotransmitters that diffuse a short distance to bind to receptors on the target cell
 Neurotransmitters play a role in sensation, memory, cognition, and movement

Fig. 45-2b
Neuron
(d) Synaptic signaling
Neurosecretory cell
Blood vessel
(e) Neuroendocrine signaling
Synapse
Response
Response

 Neurohormones are a class of hormones that originate from neurons in the brain and diffuse through the bloodstream
 Pheromones are chemical signals that are released from the body and used to communicate with other individuals in the species
 Pheromones mark trails to food sources, warn of predators, and attract potential mates

Fig. 45-3
Water-soluble Lipid-soluble
0.8 nm
Polypeptide:
Insulin
Steroid:
Cortisol
Amine:
Epinephrine
Amine:
Thyroxine

 Signaling by any of these hormones involves three key events:

Reception


Signal transduction
Response

Fig. 45-5-1
Watersoluble hormone
Signal receptor
TARGET
CELL
Transport protein
Signal receptor
Fat-soluble hormone
(a)
NUCLEUS
(b)

Fig. 45-5-2
Watersoluble hormone
Fat-soluble hormone
Transport protein
Signal receptor
TARGET
CELL
OR
Signal receptor
Cytoplasmic response Gene regulation
Cytoplasmic response
Gene regulation
(a)
NUCLEUS
(b)

Fig. 45-10
Major endocrine glands:
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Adrenal glands
Testes
Pancreas
Kidney
Ovaries
Organs containing endocrine cells:
Thymus
Heart
Liver
Stomach
Kidney
Small intestine

Fig. 45-11
–
Pathway
Stimulus
Endocrine cell
Blood vessel
Example
Low pH in duodenum
S cells of duodenum secrete secretin ( )
Target cells
Response
Pancreas
Bicarbonate release

Insulin and Glucagon: Control of Blood Glucose
 Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis
 The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin

Fig. 45-12-5
Body cells take up more glucose.
Blood glucose level declines.
Liver takes up glucose and stores it as glycogen.
Insulin
Beta cells of pancreas release insulin into the blood.
STIMULUS:
Blood glucose level rises.
Blood glucose level rises.
Liver breaks down glycogen and releases glucose.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
STIMULUS:
Blood glucose level falls.
Alpha cells of pancreas release glucagon.
Glucagon

Target Tissues for Insulin and Glucagon
 Insulin reduces blood glucose levels by



Promoting the cellular uptake of glucose
Slowing glycogen breakdown in the liver
Promoting fat storage
 Glucagon increases blood glucose levels by


Stimulating conversion of glycogen to glucose in the liver
Stimulating breakdown of fat and protein into glucose

 Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells
 Type II diabetes mellitus (non-insulindependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors

Concept 45.3: The endocrine and nervous systems act individually and together in regulating animal physiology
 Signals from the nervous system initiate and regulate endocrine signals

Coordination of Endocrine and Nervous Systems in Invertebrates
 In insects, molting and development are controlled by a combination of hormones:



A brain hormone stimulates release of ecdysone from the prothoracic glands
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

Fig. 45-13-3
Brain
PTTH
Prothoracic gland
Ecdysone
Juvenile hormone
(JH)
Low
JH
Neurosecretory cells
Corpus cardiacum
Corpus allatum
EARLY
LARVA
LATER
LARVA PUPA ADULT

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

Fig. 45-14
Pineal gland
Cerebellum
Spinal cord
Cerebrum
Thalamus
Hypothalamus
Pituitary gland
Posterior pituitary
Hypothalamus
Anterior pituitary

Table 45-1b

Table 45-1c

Table 45-1d

 Oxytocin induces uterine contractions and the release of milk
 Suckling sends a message to the hypothalamus via the nervous system to release oxytocin, which further stimulates the milk glands
 This is an example of positive feedback, where the stimulus leads to an even greater response

Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

Fig. 45-15
Hypothalamus
Neurosecretory cells of the hypothalamus
Posterior pituitary
HORMONE ADH Oxytocin
TARGET Kidney tubules Mammary glands, uterine muscles
Axon
Anterior pituitary

Hormone Cascade Pathways
 A hormone can stimulate the release of a series of other hormones, the last of which activates a nonendocrine target cell; this is called a hormone cascade pathway
 The release of thyroid hormone results from a hormone cascade pathway involving the hypothalamus, anterior pituitary, and thyroid gland
 Hormone cascade pathways are usually regulated by negative feedback

Fig. 45-18-3
–
Pathway
Stimulus Cold
Example
Sensory neuron
Neurosecretory cell
Hypothalamus secretes thyrotropin-releasing hormone (TRH )
Blood vessel
–
Anterior pituitary secretes thyroid-stimulating hormone (TSH or thyrotropin )
Thyroid gland secretes thyroid hormone
(T
3 and T
4
)
Target cells
Response
Body tissues
Increased cellular metabolism

Fig. 45-21
Stress
Adrenal medulla
Spinal cord
Nerve signals
Nerve cell
Releasing hormone
ACTH
Hypothalamus
Anterior pituitary
Blood vessel
Adrenal gland
Kidney
(a) Short-term stress response
Effects of epinephrine and norepinephrine:
1. Glycogen broken down to glucose; increased blood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
5. Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity
Adrenal cortex
(b) Long-term stress response
Effects of mineralocorticoids:
Effects of glucocorticoids:
1. Retention of sodium 1. Proteins and fats broken down ions and water by kidneys and converted to glucose, leading to increased blood glucose
2. Increased blood volume and blood pressure
2. Possible suppression of immune system

Gonadal Sex Hormones
 The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins
 All three sex hormones are found in both males and females, but in different amounts

 The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system
 Testosterone causes an increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks

 Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics
 In mammals, progestins, which include
progesterone, are primarily involved in preparing and maintaining the uterus
 Synthesis of the sex hormones is controlled by
FSH and LH from the anterior pituitary

Melatonin and Biorhythms
•
 The pineal gland, located in the brain, secretes melatonin
Light/dark cycles control release of melatonin
 Primary functions of melatonin appear to relate to biological rhythms associated with reproduction

You should now be able to:
1.
2.
3.
4.
Distinguish between the following pairs of terms: hormones and local regulators, paracrine and autocrine signals
Describe the evidence that steroid hormones have intracellular receptors, while watersoluble hormones have cell-surface receptors
Explain how the antagonistic hormones insulin and glucagon regulate carbohydrate metabolism
Distinguish between type 1 and type 2 diabetes

Concept 46.1: Both asexual and sexual reproduction occur in the animal kingdom
 Sexual reproduction is the creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote
 Asexual reproduction is creation of offspring without the fusion of egg and sperm

Fig. 46-2

 In budding, new individuals arise from outgrowths of existing ones
 Fragmentation is breaking of the body into pieces, some or all of which develop into adults
 Fragmentation must be accompanied by
regeneration, regrowth of lost body parts

Parthenogenesis is the development of a new individual from an unfertilized egg

Fig. 46-3
Asexual reproduction
Female
Sexual
Generation 1 reproduction
Female
Generation 2
Male
Generation 3
Generation 4

 Sexual reproduction results in genetic recombination, which provides potential advantages:

An increase in variation in offspring, providing an increase in the reproductive success of parents in changing environments


An increase in the rate of adaptation
A shuffling of genes and the elimination of harmful genes from a population

 Sexual reproduction is a special problem for organisms that seldom encounter a mate
 One solution is hermaphroditism, in which each individual has male and female reproductive systems
 Some hermaphrodites can self-fertilize

 Individuals of some species undergo sex reversals (like Cichlids!)

Some species exhibit male to female reversal
(for example, certain oysters), while others exhibit female to male reversal (for example, a coral reef fish)

Concept 46.2: Fertilization depends on mechanisms that bring together sperm and eggs of the same species
 The mechanisms of fertilization, the union of egg and sperm, play an important part in sexual reproduction
 In external fertilization, eggs shed by the female are fertilized by sperm in the external environment

Fig. 46-5
Eggs

 In internal fertilization, sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract
 Internal fertilization requires behavioral interactions and compatible copulatory organs
 All fertilization requires critical timing, often mediated by environmental cues, pheromones, and/or courtship behavior

Ensuring the Survival of Offspring
 All species produce more offspring than the environment can handle, and the proportion that survives is quite small
 Species with external fertilization produce more gametes than species with internal fertilization





Species with internal fertilization provide greater protection of the embryos and more parental care
The embryos of some terrestrial animals develop in amniote eggs with protective layers
Some other animals retain the embryo, which develops inside the female
In many animals, parental care helps ensure survival of offspring

 A cloaca is a common opening between the external environment and the digestive, excretory, and reproductive systems
 A cloaca is common in nonmammalian vertebrates; mammals usually have a separate opening to the digestive tract

Fig. 46-10b
Uterus
Cervix
Ovaries
Oviduct
Uterine wall
Endometriu m
Follicles
Corpus luteum
Vagina

Ovaries
 The female gonads, the ovaries, lie in the abdominal cavity

Each ovary contains many follicles, which consist of a partially developed egg, called an
oocyte, surrounded by support cells
 Once a month, an oocyte develops into an ovum
(egg) by the process of oogenesis

 Ovulation expels an egg cell from the follicle

The remaining follicular tissue grows within the ovary, forming a mass called the corpus luteum
 The corpus luteum secretes hormones that help to maintain pregnancy
 If the egg is not fertilized, the corpus luteum degenerates

Oviducts and Uterus

The egg cell travels from the ovary to the uterus via an oviduct, or fallopian tube
 Cilia in the oviduct convey the egg to the
uterus, also called the womb
 The uterus lining, the endometrium, has many blood vessels
 The uterus narrows at the cervix, then opens into the vagina

Mammary Glands
 The mammary glands are not part of the reproductive system but are important to mammalian reproduction
 Within the glands, small sacs of epithelial tissue secrete milk

Fig. 46-11b
Seminal vesicle
(Rectum)
Vas deferens
Ejaculatory duct
Prostate gland
Bulbourethral gland
Vas deferens
Epididymis
Testis
Scrotum
(Urinary bladder)
(Urinary duct)
(Pubic bone)
Erectile tissue
Urethr a
Glans
Penis
Prepuce

Concept 46.4: The timing and pattern of meiosis in mammals differ for males and females
 Gametogenesis, the production of gametes by meiosis, differs in females and males
 Sperm are small and motile and are produced throughout the life of a sexually mature male

Spermatogenesis is production of mature sperm

Fig. 46-12g
In embryo
Primordial germ cell
Mitotic divisions
2n Oogonium
First polar body n
Mitotic divisions
2n
Primary oocyte
(present at birth), arrested in prophase of meiosis I
Completion of meiosis I and onset of meiosis II n Secondary oocyte, arrested at metaphase of meiosis II
Ovulation, sperm entry
Second polar body n n
Completion of meiosis
II
Fertilized egg

 Spermatogenesis differs from oogenesis:



In oogenesis, one egg forms from each cycle of meiosis; in spermatogenesis four sperm form from each cycle of meiosis
Oogenesis ceases later in life in females; spermatogenesis continues throughout the adult life of males
Oogenesis has long interruptions; spermatogenesis produces sperm from precursor cells in a continuous sequence

Fig. 46-14a
(a) Control by hypothalamus
Hypothalamu s
GnRH
Anterior pituitary
FSH LH
(b) Pituitary gonadotropins in blood
–
+
–
Inhibited by combination of estradiol and
Stimulated by high levels of estradiol
Inhibited by low levels of estradiol
LH
(c)
FSH
FSH and LH stimulate follicle to grow
Ovarian cycle
LH surge triggers ovulation
|
0
Growing follicle
Maturing follicle
Follicular phase
5
|
10
Ovulation
| |
14 15
Corpus luteum
Degenerating corpus luteum
Luteal phase
|
20
|
25
|
28

Fig. 46-14b
(d) Ovarian hormones in blood
Peak causes
LH surge
Estradiol
Estradiol level very low
(e) Uterine (menstrual) cycle
Endometriu m
Progesterone
Ovulation
Progesterone and estradiol promote thickening of endometrium
Menstrual flow phase Proliferative phase
0
|
5
|
10
|
14
|
15
Secretory phase
|
20
|
25
|
28

 Estrous cycles are characteristic of most mammals:

The endometrium is reabsorbed by the uterus


Sexual receptivity is limited to a “heat” period
The length and frequency of estrus cycles varies from species to species

Conception, Embryonic Development, and Birth
 Conception, fertilization of an egg by a sperm, occurs in the oviduct

The resulting zygote begins to divide by mitosis in a process called cleavage
 Division of cells gives rise to a blastocyst, a ball of cells with a cavity

Fig. 46-15
3 Cleavage
4 Cleavage continues
Ovary
2 Fertilization
1 Ovulation
(a) From ovulation to implantation
Endometrium
Inner cell mass
Cavity
Blastocyst
(b) Implantation of blastocyst
Uterus
Endometrium
5 The blastocyst implants
Trophoblast





After blastocyst formation, the embryo implants into the endometrium
The embryo releases human chorionic
gonadotropin (hCG), which prevents menstruation
Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus
Duration of pregnancy in other species correlates with body size and maturity of the young at birth

Fig. 46-16
Uterus
Placenta
Umbilical cord
Chorionic villus, containing fetal
Maternal blood pools
Fetal arteriole
Fetal venule
Umbilical cord
Maternal arteries
Maternal veins
Maternal portion of placenta
Fetal portion of placenta
(chorion)
Umbilical arteries
Umbilical vein

 Splitting of the embryo during the first month of development results in genetically identical twins
 Release and fertilization of two eggs results in fraternal and genetically distinct twins

Fig. 46-17
(a) 5 weeks
(b) 14 weeks (c) 20 weeks

Fig. 46-19-4
1
Dilation of the cervix
Placenta
Umbilical
Uterus
Cervix
2
Expulsion: delivery of the infant
Uterus
Placenta
(detaching)
Umbilical cord
3
Delivery of the placenta

 Birth, or parturition, is brought about by a series of strong, rhythmic uterine contractions

First the baby is delivered, and then the placenta
 Lactation, the production of milk, is unique to mammals

Fig. 47-2


Development is determined by the zygote’s genome and molecules in the egg called cytoplasmic determinants
 Cell differentiation is the specialization of cells in structure and function
 Morphogenesis is the process by which an animal takes shape

Concept 47.1: After fertilization, embryonic development proceeds through cleavage, gastrulation, and organogenesis
 Important events regulating development occur during fertilization and the three stages that build the animal’s body

Cleavage: cell division creates a hollow ball of cells called a blastula


Gastrulation: cells are rearranged into a three-layered gastrula
Organogenesis: the three layers interact and move to give rise to organs

Fig. 47-3-5
Basal body
(centriole)
Sperm head
Acrosome
Jelly coat
Sperm-binding receptors
Sperm plasma membrane
Sperm nucleus
Acrosomal process
Fertilization envelope
Actin filament
Fused plasma membranes
Cortical granule
Hydrolytic enzymes
Perivitelline space
Vitelline layer
Egg plasma membrane EGG CYTOPLASM

 In mammals the first cell division occurs 12–36 hours after sperm binding

The diploid nucleus forms after this first division of the zygote

Cleavage
 Fertilization is followed by cleavage, a period of rapid cell division without growth
 Cleavage partitions the cytoplasm of one large cell into many smaller cells called blastomeres
 The blastula is a ball of cells with a fluid-filled cavity called a blastocoel

Fig. 47-6
(a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula

Fig. 47-8-6
0.25 mm 0.25 mm
Animal pole Blastocoel
Zygote 2-cell stage forming
4-cell stage forming
8-cell stage
Vegetal pole Blastula
(cross section)





Cell division is slowed by yolk
Holoblastic cleavage, complete division of the egg, occurs in species whose eggs have little or moderate amounts of yolk, such as sea urchins and frogs
Meroblastic cleavage, incomplete division of the egg, occurs in species with yolk-rich eggs, such as reptiles and birds
Gastrulation rearranges the cells of a blastula into a three-layered embryo, called a gastrula, which has a primitive gut

 The three layers produced by gastrulation are called embryonic germ layers



The ectoderm forms the outer layer
The endoderm lines the digestive tract
The mesoderm partly fills the space between the endoderm and ectoderm
Video: Sea Urchin Embryonic Development

 Gastrulation in the sea urchin embryo



The blastula consists of a single layer of cells surrounding the blastocoel
Mesenchyme cells migrate from the vegetal pole into the blastocoel
The vegetal plate forms from the remaining cells of the vegetal pole and buckles inward through invagination

 Gastrulation in the sea urchin embryo

The newly formed cavity is called the archenteron

This opens through the blastopore, which will become the anus

Fig. 47-14
ECTODERM MESODERM
Epidermis of skin and its derivatives (including sweat glands, hair follicles)
Epithelial lining of mouth and anus
Cornea and lens of eye
Nervous system
Sensory receptors in epidermis
Adrenal medulla
Tooth enamel
Epithelium of pineal and pituitary glands
Notochord
Skeletal system
Muscular system
Muscular layer of stomach and intestine
Excretory system
Circulatory and lymphatic systems
Reproductive system
(except germ cells)
Dermis of skin
Lining of body cavity
Adrenal cortex
ENDODERM
Epithelial lining of digestive tract
Epithelial lining of respiratory system
Lining of urethra, urinary bladder, and reproductive system
Liver
Pancreas
Thymus
Thyroid and parathyroid glands

Developmental Adaptations of Amniotes
 Embryos of birds, other reptiles, and mammals develop in a fluid-filled sac in a shell or the uterus
 Organisms with these adaptations are called amniotes

 During amniote development, four
extraembryonic membranes form around the embryo:

The chorion functions in gas exchange



The amnion encloses the amniotic fluid
The yolk sac encloses the yolk
The allantois disposes of waste products and contributes to gas exchange

Fig. 47-15
Amnion
Embryo
Amniotic cavity with amniotic fluid
Shell
Chorion
Allantois
Albumen
Yolk sac
Yolk
(nutrients)

Mammalian Development







The eggs of placental mammals



Are small and store few nutrients
Exhibit holoblastic cleavage
Show no obvious polarity
Gastrulation and organogenesis resemble the processes in birds and other reptiles
Early cleavage is relatively slow in humans and other mammals
At completion of cleavage, the blastocyst forms
A group of cells called the inner cell mass develops into the embryo and forms the extraembryonic membranes
The trophoblast, the outer epithelium of the blastocyst, initiates implantation in the uterus, and the inner cell mass of the blastocyst forms a flat disk of cells
As implantation is completed, gastrulation begins

Fig. 47-16-5
Uterus
Endometrial epithelium
(uterine lining)
Inner cell mass
Trophoblast
Blastocoel
Maternal blood vessel
Expanding region of trophoblast
Amniotic cavity
Epiblast
Hypoblast
Yolk sac (from hypoblast)
Extraembryonic mesoderm cells
(from epiblast)
Chorion (from trophoblast)
Expanding region of trophoblast
Epiblast
Hypoblast
Trophoblast
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolk sac
Extraembryonic mesoderm
Allantois