biology

Human placental lactogen

Human placental lactogen is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Human placental lactogen rather than just read about it. In short: Human placental lactogen (hPL), also called human chorionic somatomammotropin (hCS) or human chorionic somatotropin, is a polypeptide placental hormone, the human form of placental lactogen (chorionic somatomammotropin). Its structure and function are similar to those of human growth hormone.

Key takeaways

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Reproduce the core statement of Human placental lactogen from memory before moving on to harder problems.

Reference excerpt

Human placental lactogen (hPL), also called human chorionic somatomammotropin (hCS) or human chorionic somatotropin, is a polypeptide placental hormone, the human form of placental lactogen (chorionic somatomammotropin). Its structure and function are similar to those of human growth hormone. It modifies the metabolic state of the mother during pregnancy to facilitate energy supply to the fetus. hPL has anti-insulin properties. hPL is a hormone secreted by the syncytiotrophoblast during pregnancy. Like human growth hormone, hPL is encoded by genes on chromosome 17q22-24. It was identified in 1963.

Structure hPL molecular mass is 22 125 Da and contains single chain consisting of 191 amino acid residues that are linked by two disulfide bonds and the structure contains 8 helices. A crystal structure of hPL was determined by X-ray diffraction to a resolution of 2.0 Å.

Levels hPL is present only during pregnancy, with maternal serum levels rising in relation to the growth of the fetus and placenta. Maximum levels are reached near term, typically to 5–7 mg/L. Higher levels are noted in patients with multiple gestation. Little hPL enters the fetal circulation. Its biological half-life is 15 minutes. Some women with higher BMI show lower levels of placental lactogen, but whether prenatal health behaviors influence hPL levels or if hPL influences infant birth weight is uncertain.

Physiologic function hPL affects the metabolic system of the maternal organism in the following manners:

In a bioassay, hPL mimics the action of prolactin, yet it is unclear whether hPL has any role in human lactation. Metabolic: ↓ maternal insulin sensitivity (insulin resistance), leading to an increase in maternal blood glucose levels. ↓ maternal glucose utilization, which helps ensure adequate fetal nutrition (the mother responds by increasing beta cells). Chronic hypoglycemia leads to a rise in hPL. ↑ lipolysis with the release of free fatty acids. With fasting and release of hPL, free fatty acids become available for the mother as free fatty acids do not cross the placenta, so that relatively more glucose can be utilized by the fetus. With sustained fasting, maternal ketones formed from free fatty acids can cross the placenta and be used by the fetus. These functions help support fetal nutrition even in the case of maternal malnutrition. hPL is a potent agonist of the prolactin receptor and a weak agonist of the growth hormone receptor.

Prolactin-like activity hPL has been found to bind to the prolactin receptor with equal affinity to that of prolactin in rabbit milk fat globule membrane, and hPL and prolactin have been found to possess very similar lactogenic activity in vitro in mouse and rat mammary gland explants. In addition, hPL has been found to stimulate DNA synthesis in human mammary fibroadenoma cells transplanted into mice, which suggests that hPL promotes the growth of the human mammary gland similarly to prolactin. As hPL circulates at concentrations that are 100-fold higher than those of prolactin during pregnancy, these findings suggest that hPL may play an important role in human mammogenesis during this time. However, the relative affinities of hPL and prolactin for the human prolactin receptor have yet to be published and the effects of hPL on normal human mammary epithelial tissue have not yet been investigated, and so a definitive role of hPL in human mammary gland development during pregnancy has not been established at present.

Growth hormone-like activity hPL has weak actions, similar to those of growth hormone, causing the formation of protein tissues in the same way that growth hormone, but 100 times more hPL than growth hormone is required to promote growth. However, hPL has a blood level of more than 50 times that of hGH, hence its effects must not be ignored. An enhancer for the human placental lactogen gene is found 2 kb downstream of the gene and participates in the cell-specific control gene expression.

Clinical measurement While hPL has been used as an indicator of fetal well-being and growth, other fetal testing methods have been found to be more reliable. Also, normal pregnancies have been reported with undetectable maternal levels of hPL.

See also Placental lactogen in other species Pregnancy hormones Somatotropin family

References

"RCSB Protein Data Bank - Structure Summary for 1Z7C - Crystal Structure of Human Placental Lactogen". "Human Chorionic Somatomammotropin Enhancer Function Is Mediated by Cooperative Binding of TEF-1 and CSEF-1 to Multiple, Low-Affinity Binding Sites". Archived from the original on 2008-07-05.

Further reading Speroff L, Glass RH, Kase NG (1999). Clinical gynecologic endocrinology and infertility (Sixth ed.). Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 0-683-30379-1.

External links Human+Placental+Lactogen at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

Illustrations

Worked examples

Example 1 — a first encounter with Human placental lactogen

Start with the simplest possible case. Write down what Human placental lactogen claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Human placental lactogen before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Human placental lactogen ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Human placental lactogen

In research: Human placental lactogen appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Human placental lactogen in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Human placental lactogen is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 17, Hormones of the placenta, Hormones of the pregnant female, so understanding it makes those chapters shorter.
In everyday life: Look for Human placental lactogen outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Human placental lactogen in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Human placental lactogen means in your own words.
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Frequently asked questions

What is Human placental lactogen in simple terms?

Why does Human placental lactogen matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Human placental lactogen?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Human placental lactogen.