Transcript Cell Differentiation

Cell Differentiation
• All cells in an embryo descend from the same
zygote and have the same genes
• ________________________: Certain groups
of genes are activated in some cells but not in
others
• Genes are not lost, just inactivated
• Different cell lineages become specialized in
composition, structure, and function
• Body has ______ differentiated cell types
Cell Communication in Development
• __________________: signaling molecules
produced by master genes
– Secreted by cells
– Effect on target cell is proportional to its
concentration
• Embryonic induction occurs when embryonic
cells produce signals that alter the behavior of
neighboring cells
• Example: cells at dorsal lip
Morphogenesis
• Orderly changes result in
specialized tissues and early
organs
• Cells ____________
• Whole sheets of cells expand
and fold
• Programmed cell death
(_____________) sculpts body
parts
Cell migration
ectoderm at gastrula stage
neural groove
ectoderm
neural tube
Morphogenesis:
Neural tube
formation
7. Organ Formation
• Newly forming cells increasing specialized
in structure and function
• Tissues and organs mature in size, shape
and formation
__________ __________
• Development fate of embryonic cell
lineages changes upon exposure to gene
products from adjacent tissues
• Cells behave as if they have positional
memory
• Demonstrated experimentally by
transplanting embryonic cells
Cell Memory:
_____________________
Transplant organized formation of second set
of structures
Cell Memory:
Chick Wing Development
A. Remove a wing
bud’s AER, and wing
development stops.
mesoderm of
developing
forelimb in a
chick embryo
B. Graft a bit of leg
mesoderm beneath
the AER and part of
a leg—even some
toes—develops.
AER
removed
graft of wing
mesoderm
from leg
leg forms
Morphogens
• Substance governing the pattern of tissue
development
• Spreads from a localized source and forms a
concentration gradient across a developing tissue
• Gradient helps a cell chemically assess its position
in the embryo and how it should differentiate
• Influences which genes are turned on or off
________ ___________
• Process through which certain body parts form
in a specific place
• Starts with ________________________
(where cells are located relative to the original
maternal cytoplasm)
• Classes of master genes activated in
sequence
• Interactions among master genes are guided
by regulatory proteins
• Gene products are spatially organized in the
embryo
Similar Master Genes
• Diverse animals use similar or the same
master genes to govern development
• May help explain why
____________________________________
• The relatively small number of master genes
constrains variation
The Reproductive System
• Gonads – _________________________
– Testes in males
– Ovaries in females
• Gonads produce ____________ (sex cells)
and secrete _____________
– Sperm – male gametes
– Ova (eggs) – female gametes
Male Reproductive System
PROSTATE
GLAND
• Testes
EJECULATORY DUCT
SEMINAL
VESICLE
urinary bladder
• Duct system
– Epididymis
– Vas deferens
– Urethra
URETHRA
urethra
anus
anterior
BULBOURETHRAL
GLAND
posterior
VAS DEFERENS
PENIS
erectile tissue
TESTIS
EPIDIDYMIS
Figure 16.2b
Male Reproductive System
• Accessory organs
PROSTATE
GLAND
– Seminal vesicle
– Prostate gland
– Bulbourethral gland
EJECULATORY DUCT
SEMINAL
VESICLE
urinary bladder
URETHRA
urethra
anus
• External genitalia
– Penis
– Scrotum
anterior
BULBOURETHRAL
GLAND
posterior
VAS DEFERENS
PENIS
erectile tissue
TESTIS
EPIDIDYMIS
Testes
• Males have 2 gonads
called testes
• __________________
• Few degrees cooler than
body temperature for
sperm development
• Seminiferous tubules
– Tightly coiled structures
– Function as sperm-forming
factories
• Produce _____________
Figure 16.1
Epididymis
• Comma-shaped,
tightly coiled tube
• Sperm travels from testes to epididymis
• Function: to mature and store sperm cells
– At least ____________________
• Expels sperm with the contraction of muscles in
the epididymis walls to the vas deferens
Vas Deferens
• Carries sperm from epididymis to the ejaculatory
duct
• _________________ – cutting of the vas deferens
at the level of the testes to prevent transportation
of sperm
PROSTATE
GLAND
EJECULATORY DUCT
SEMINAL
VESICLE
urinary bladder
URETHRA
urethra
anus
anterior
BULBOURETHRAL
GLAND
posterior
VAS DEFERENS
PENIS
erectile tissue
TESTIS
EPIDIDYMIS
Urethra
• Extends from the base of the urinary bladder
to the tip of the penis
• Carries ______________________
• Sperm enters from the ejaculatory duct
Semen = _________ + ________
• Secretions from
epididymis aid sperm
maturation
PROSTATE
GLAND
SEMINAL
VESICLE
urinary bladder
• Other secretions come
from:
– Seminal vesicle
URETHRA
urethra
anus
anterior
– Prostate gland
BULBOURETHRAL
GLAND
posterior
VAS DEFERENS
PENIS
erectile tissue
– Bulbourethral gland
EJECULATORY DUCT
TESTIS
EPIDIDYMIS
Seminal Vesicles
• Located at the base of the bladder
• Produces a thick, yellowish secretion (60%
of semen)
– Fructose (sugar), Why?
– Vitamin C
– Prostaglandins
– Other substances that nourish and activate
sperm
Prostate Gland
• Encircles the upper part of the urethra
• Secretes a milky fluid
– Helps to activate sperm
– Enters the urethra through several small ducts
• Functions to ___________________________
Bulbourethral Glands
• Pea-sized gland
• Produces a thick, clear mucus
– Cleanses the urethra of acidic urine
– Lubricates urethra so sperm can get through
Semen
• Mixture of sperm and accessory gland
secretions
• Advantages of accessory gland secretions
– Fructose provides energy for sperm cells
– Alkalinity of semen helps neutralize the acidic
environment of vagina
– Semen inhibits bacterial multiplication
– Elements of semen enhance sperm motility
External Genitalia
• Scrotum
– Divided sac of skin outside the abdomen
– Maintains testes at 3°C lower than normal body
temperature to protect sperm viability
• Penis
– Delivers sperm into the female reproductive
tract
– Internally, three areas of spongy erectile tissue
around the urethra
Sperm Formation: Seminiferous
Tubules
vas
deferens
seminal vesicle
prostate gland
bulbourethral
gland
urethra
penis
epididymis
semini ferous
tubule
testis
Spermatogenesis
• Production of sperm cells
• Begins at puberty and continues throughout life
• In the seminiferous tubules (inside testes)
• Spermatogonium (2n) divides by mitosis to form
primary spermatocyte (2n)
• Meiosis produces haploid spermatids
• Spermatids mature to become sperm
• Spermatogenesis takes 64 to 72 days
Anatomy of Mature Sperm
•
•
•
•
The only human flagellated cell
DNA is found in the head
Little cytoplasm
48-72 hour lifespan (up to 5 days)
Figure 16.5b
Testosterone Production
• Produced in Testes by ______________
• Functions of testosterone
– Stimulates reproductive organ development
– Underlies sex drive
– Helps develop and maintain sexual behavior
– Causes _____________________________
• Deepening of voice
• Increased hair growth
• Enlargement of skeletal muscles
• Thickening of bones
Regulation of Male Androgens (Sex
Hormones)
Figure 16.6
Hormone Controls
• Gonadotropin-releasing hormone (_______)
from the hypothalamus stimulates the
secretion of LH and FSH
• Luteinizing hormone (____) is released by the
anterior pituitary and stimulates testosterone
produced
• Follicle-stimulating hormone (_____)
stimulates the production of sperm beginning
at ____________