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Question
Cross-bridge formation occurs when myosin heads attach to actin molecules located in the thin filaments.
Answer
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Related questions
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The Leydig cells of the testes constitute a blood-testis barrier that prevents autoimmune destruction of the sperm.
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Secretion of LH is inhibited by
A. high concentrations of inhibin.
B. rapidly rising concentrations of estradiol.
C. high concentrations of testosterone.
D. decreasing concentrations of progesterone.
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Women do not enter a refractory period following orgasm and are capable of multiple orgasms.
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Which of the following is a precursor to melatonin synthesis?
A. tryptophan
B. serotonin
C. tyrosine
D. Both tryptophan and serotonin are correct.
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In males androgens are required for
A. initiation of spermatogenesis at puberty.
B. regression of the wolffian ducts during embryonic development.
C. maintenance of accessory sex organs.
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The role of melatonin in puberty of humans is well established and critical.
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Pubic and axillary hair growth at puberty is from increased secretion of
A. anterior pituitary gonadotropins.
B. estrogen and testosterone from the onads.
C. androgens from the adrenal cortex.
D. melatonin from the pineal gland.
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Epiphyseal growth in males is stimulated by estrogen.
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The rate at which GnRH is secreted from the hypothalamus determines whether LH or FSH is secreted from the anterior pituitary.
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A male with 5 alpha-reductase deficiency will have male internal sex organs but more female appearing external genitals.
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Males lacking testosterone receptors would
A. develop as genotypic females.
B. have testes and female external genitalia.
C. lack gonads.
D. have male internal genitalia.
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Treating a male fetus with antibodies to DHT would prevent development of the epididymides.
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Female accessory sex organs develop from the mesonephric ducts.
Q:
How many chromosomes are found in a normal human cell?
A. 23
B. 23 pair
C. 46
D. Both 23 pair and 46 are correct.
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Cryptorchid males do not produce testosterone.
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Epigenetic changes can not be passed on to a zygote.
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The stimulus of sucking causes release of prolactin-releasing hormone via a neuroendocrine reflex.
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Infants that are breastfed receive which of the following from the mother?
A. IgA
B. IgG
C. IgF
D. IgE
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What hormone is secreted by the anterior pituitary that stimulates production of milk proteins?
A. oxytocin
B. growth hormone
C. MSH
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Genetic screening of newborns using only a drop of blood can determine which of the following genetic disorders?
A. hypothyroidism
B. cystic fibrosis
C. sickle cell anemia
D. All of the choices are correct.
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What hormone may play a role in reducing the size of the uterus following delivery?
A. progesterone
B. prostaglandin
C. oxytocin
D. prolactin
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DHEAS travels from the fetal adrenal cortex to the placenta where it is converted into oxytocin.
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Cortisol from the fetal adrenal gland will stimulate maturation of the lungs and production of surfactant.
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Blood within the umbilical ___________ contain(s) high concentrations of fetal waste products.
arteries
B. veins
C. capillaries Chapter 20
Q:
A ball of about eight cells formed about 50 to 60 hours after fertilization is called a
A. zygote.
B. morula.
C. blastocyst.
D. embryo.
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The progressive fusion of the acrosomal membrane with the plasma membrane of the sperm is called the
A. spermatogenesis.
B. acrosomal reaction.
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After meiosis I in males, ________ are formed.
A. primary spermatocytes
B. secondary spermatocytes
C. spermatids
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Hypocalcemia enhances the excitability of nerves and muscles because of the ____ permeability of the cell membrane to ___.
A. increased, K+
B. decreased, K+
C. increased, Na+
D. decreased, Na+
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Cells synthesizing hydroxyapatite in bones are termed as
A. osteoblasts.
B. osteoclasts.
C. osteocytes.
D. osteosarcoma cells.
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Bone resorption is produced by the action of _____________, which return bone calcium and phosphate to the blood.
A. osteoblasts
B. osteoclasts
C. osteocytes
D. calcitonin